I built this pen in 2007 and it has needed little maintenance over the last four years. However since I built it four years ago I do not have any construction photos, so I will do my best to explain and provide sketches. This instructable will tell you how to build a similar pen, but not everything. The design of your pen will depend on how many turtles you have and what species. You will need to be a skilled builder and designer to accomplish this. I should also note that this is not a cheap pen, see the word luxury in the title. Mine is approximately 56 sq.ft and cost a couple hundred dollars to build.

Tools Needed:
-Powerdrill
-Large Drillbit
-Hacksaw
-Utility Knife
-Scissors
-Bull-Nose Cutters or Pliers
-Shovel
-Sledgehammer
-Rubber Mallet(optional)
-Pickaxe(optional)

Materials Needed:
-PVC Pipe; 3/4" and 1 1/2"
-PVC Pipe Fittings; Tees, Elbows, Couplings
-PVC Glue
-Fiber Roof-Tiles
-Plastic Mesh
-Zip-Ties
-Self-Drill Screws; 1/2" and 3/4"
-Hinges
-Topsoil and Mulch
-Assorted Plants
-Paving Stones(optional)
-Old pieces of Wood
-Concrete(optional)
-Metal Mesh(optional)

Step 1: Planning

Now before you begin designing your turtle pen, you need to do a bit a research on your specific turtle species.
Things to learn: (All examples are for Three-Toed Box Turtles)
-Male to female ratio, ex. 1:2
-Space needed for each turtle, ex. ~16 sq.ft
-Poisonous items, ex. cedar wood, sweet pea, ivy etc.(http://www.tortoise.org/general/poisonp.html )
-Other odd facts that may be particular to your turtle

After you find out that information you should have a general idea of how big your turtle pen should be; now you can choose a location to build your pen. One thing to consider is amounts of shade and sunlight; you want your pen to get plenty of sun but still be shaded for a good part of the day, consider a spot near a tree. I would avoid placing your pen near your house or other building because when pest control comes(if they do) they spray poison around the perimeter of your house, and you don't want any of that to get near your pen. You should also consider access to a hose(something I didn't think of) to avoid having to pull a hose all the way across your yard.

Once you have decided on a location for your pen you can take some measurements, and begin designing the layout of your pen, and making a list of supplies(Make a trip to your local Home Depot or hardware store and take notes of what they have before doing this). You can go ahead and buy everything now or buy it throughout the process.

Step 2: Excavation

Now for the most labor intensive part of the process. Begin by plotting out the perimeter of your pen in the location where you want to build it; you can use stakes and string or whatever. Once you have it all marked out, grab a shovel and begin digging around the inside line of the perimeter. You want to dig down about 6-10 inches, depending on how soft the ground is(softer=go deeper). After making a nice trench around the outside, begin to dig in the middle. the middle is not as crucial as the edges. If your ground is very hard, use a hose to soften it, or use the optional pickaxe.

Step 3: Walls

The walls will be constructed out of the roofing tiles. Measure out how many you will need to make it all the way around. Be sure to account for an overlap when connecting two together, I used 1-2 bumps as an overlap. For the corners, drive a long piece of 1 1/2" PVC Pipe as a stake, it needs to be about 12 Inches longer than the height of the walls. But drive them in so they are about 2 inches less than the height of the walls. Cut the roofing tiles with the utility knife; it will take several passes before you make it all the way through. When you have the pieces cut, lay them down on the ground and use the 1/2" screws to attach any overlaps together(you should only need to use 2). Then place the complete walls in the pit you previously made, the bottoms of the walls will be below ground level. Attach* both ends to the PVC stakes in the corners. Do this for all the walls.

Optionally, you can place paving stones around the inside perimeter, to stop any attempts at digging out. I decided not to because the ground was so hard they wouldn't be able to dig through it anyway.

*When you're screwing through the roof tiles, be careful that you don't rip right through the tile itself

Step 4: Pond(optional)

This step is completely optional, whether you want to add a pond is up to you.

Decide where in the cage and how big you want it to be. Choose one end or a corner; DO NOT PLACE IT IN A WAY THAT IT BLOCKS OFF A SECTION OF THE CAGE!!! You don't want a turtle to be forced to cross the pond to get somewhere, as it could pose a threat. Once you have decided where to place your pond, decide on its architecture; be sure to have shallow edges for easy access and you don't want to make it any more than 5-6 inches deep. Then you can begin digging/adding dirt; sculpt at least an inch or two deeper than your design to account for the concrete. Next, cut and bend some metal mesh into the shape of your pond; this serves as miniature rebar. Place it in the hole, you will most likely have to use some small scraps of wood to support it slightly, so it is 1/2" or so off the ground. Mix the concrete and pour it in; spread it around so it covers evenly, and is in the shape you want it. After it hardens, thoroughly wash it and scrub it two remove any harmful chemicals from the concrete.

Another optional extra is adding a pump to supply flowing water. If you do want to add a pump, build in a sump at the lowest point in your pond. I had a solar powered pump but it has broken several times due to clogs.

Step 5: Frame

The first part to building the frame is calculate how big to make it. You can either calculate it from your design or physically measure from your walls. You want to know the needed length and width from the inside of the walls. Subtract the length that each elbow and tee adds from the total length to find how long to cut the PVC Pipe. Here we are using the 1 1/2" pipe. Use the hacksaw to cut all the needed pieces to length and clean up the ends by pulling off all the bits a plastic bristliy bits(if you have cut PVC before then you know what I'm talking about). I suggest moving to a garage floor for the gluing process, as a flat surface will help get the whole frame flat; also having a rubber mallet handy would be good. To glue, swab some PVC glue around the end of the pipe and slide whichever fitting on the end. The glue hardens fast, so you may need to use a rubber mallet to ensure it got all the way on. As your frame begins to take shape, use the flat ground to ensure that your frame is sitting flat with no corners lifting off the ground. If you see a corner lifting up, have either yourself or a buddy hold down the opposite side and give the lifting corner a wack of the mallet.

After you have the basic frame done, cut a piece of PVC the same length as the entire frame. This piece will serve as the mount for the lids. You will have to drill some holes on one side of the pipe, in order to screw it onto the frame. Use the 3/4" screws to screw it on.

Step 6: Lids

How many and how big your lids/door flaps are will depend on your pen. I suggest that if your pen is wider than 30" then you should split the width across two lids. I also suggest you make all the lid frames then check them all on the frame before finishing them off.
Essentially the lids are just PVC rectangles, made from the 3/4" pipe. Measure and calculate the size of each rectangle, then subtract the added length of the elbows to get the length of the pipe pieces. When gluing them be careful that they stay flat, just like you did with the frame. Once you have them glued together, you can use the scissors to cut the plastic mesh to lay over each rectangle. Attach the mesh with the zip-ties*. Then use the 1/2" screws to attach the hinges on one side of the rectangle. Put them about about a quarter of the length in from each side.

*The zip-ties have been a pain, as they continue to weaken and brake off over-time; if you can, find and use UV protected zip-ties or come up with a better solution

Step 7: Frame Installation

Carry the completed frame to the walls and set it in. It should rest on top of the PVC posts in the corners, being just about level with the walls all around. Use the 3/4" screws to attach the walls to the frame; put a screw in once every 2 bumps.

Step 8: Landscaping

Now that the pen is structurally sound, we can add in some dirt and plants. Buy several bags of generic topsoil and mulch. DO NOT BUY ANYTHING WITH FERTILIZER!!! You can even buy organic if you wish, and be careful that you don't buy a type of mulch that is poisonous to your turtles. Fill in the pit till the ground level in the pen is a few inches above that outside the pen, stopping occasionally to stomp down and compact the dirt some. You can choose to either mix the topsoil and mulch together before putting it in or put the mulch on top of the topsoil, whatever floats your boat. Buy a selection of tall grasses and ferns and whatnot, as long as they aren't poisonous. Plant the plants in whatever arrangement you want. I chose to keep the plants close together so they weren't trampled and killed right away. I also let whatever weeds grow, that grow; they just make it more like a forest floor.
Note that it may take up to a year for the plants to settle/spread and the dirt to settle and look like a forest floor.

Step 9: Lid Installation

Take your already fabricated lids and lay them down in place on top of the frame. Place them all on there at once and make sure there is a small gap between each one so they don't get stuck. Use the 1/2" screws to attach the other end side of the hinges to the middle PVC pipe. Test each lid by lifting and making sure it comes up straight and doesn't conflict with its neighbor lids. I did not put latches on, put if you feel its necessary then go ahead.

Step 10: Final Touches

Use some old scraps of plywood as lean-to's to provide easy hiding spots, add food dishes, and water bowls(if you didn't build a pond). I also use some pieces of 1/4" Plywood to place on top for shade and rain cover. In the winter I fill one end of the cage with leaves(you can see some leftovers in some of the pictures) and cover the top with a tarp for hibernation.