I always wanted to build a greenhouse so when I found an article explaining how to build one for $50, I immediately started to build mine.

The first problem I encountered was that the design was not appropriate for heavy snow falls. It would collapse under a few inches of wet snow. So I decided to alter the design a little to make it more sturdy and prevent any snow accumulation at the top. The ogive shape adds strength to the top part of the greenhouse while making the roof angle steeper.

I should also mention that it cost me more than $50. Part of if is that I didn't have any wood lying around. Another price increase came from the fact that I had to use thicker wood. The last bump in my total cost comes from the fact that Whitehorse is a pretty isolated town and you get to pay more for every piece of lumber/hardware.

Step 1: Materials and Tools

12 foot long 2x4s. You'll need at least 12 of those. Take the pressure treated wood if you want your greenhouse to last more than a few years. You can usually find ACQ of PWF lumber at the hardware store.
6 mil plastic sheet. You will need at least 22 feet wide by 16 feet long. If you can't find anything larger than 10 feet, you can tape 2 sheets with construction tape.
Some plywood to hold the 2x4 together.
A bunch of screws. Drywall screws work well and you can get a lot for cheap.
A bag of tie-wraps. They need to be long enough to wrap around a 2x2.
3/4" Schedule 40 PVC tubing. Take the gray one because it's resistant to UV light. You'll need 10 of them.
2 feet rebar. You will need 8 oth them to hold the pvc pipes.
45 degree PVC connectors 3/4" inside diameter. You will need 5 of them.
Optional: 6 round quick pins if you want to be able to dismantle the greenhouse easily.
4 metal fence posts
4 2 by 4 end brackets

Step 2: Build the Sides

The original plans are using 1x4 lumber. However, in Canada, you really want to upgrade to 2x4 trusses. Snow can be pretty heavy.

Start by connecting 2 PVC pipes together using a 45 degree connector. If you don't want to glue the pipes so that you can dismantle it later, use round quick pins to attach them.

Temporarily attach both ends of the assembly to each side of a 11 feet 2 by 4. This gives you a rough idea of the dimension of the side of your greenhouse.

You can now decide what size your door should be. Mine is 3 feet but you can make it larger if you want to drive a large wheelbarrow throught it. The height is also up to you.

Now that you have decided the width and height of your door, you can measure and cut all the other pieces of wood (cf drawing).

Cut some plywood, apply some glue and drill it onto the 2 by 4 boards. It will keep everything strong and square.

Drill holes in the PVC pipe in the 4 locations mentioned on the drawing and use tie-wraps to keep it even stronger.

You can now staple plastic on each sides. Cut a hole in one of them for the door.

Step 3: Attach the Sides Together

Your first task is to find a 12' by 12' space that is flat enough to put your greenhouse.

Once you found it, hammer 2 fence posts at one end. Make sure to align the posts with the vertical sides of your door. If you chose a 3 feet wide door, put your fence posts 3 feet 4 inches apart.

When you can't push the posts deeper into the ground, place one side of your greenhouse against the posts and drill holes through the 2 by 4 and use zip-ties to fasten it to the posts.

Repeat the whole thing 12 feet further to set the other side of the greenhouse. Make sure they are aligned.

Use two 12 feet 2 by 4 and screw them onto the plywood on each side using end brackets. You should end up with 2 strong beams joining both sides of your greenhouse.

Step 4: Assemble the PVC Pipes

The greenhouse is now solidly anchored to the ground but we still need to put the ribs to it.

Hammer some rebar every 3 feet from one side. Put them at an angle as we will slide the PVC tubes onto it.

Create more PVC assemblies (2 10-feet PVC tubes + connector + pins). You'll need 3 of them. Slide them on the rebar and align them the best that you can. Screw the pipes on the horizontal trusses. Fasten them with tie-wraps to prevent any movement.

A second horizontal beam is added lower on the ribs. This ensures that the plastic does not collapse through the PVC tubes during high winds and snow storms.

Another important element is the crossed wires you can see on the last picture. They create diagonals, making sure that the greenhouse stays square over time. The wires cross over the middle PVC pipe on each side.

Step 5: Cover the Pipes With Plastic

Time to cover the greenhouse.

Use your 22' by 16' plastic film and wrap both ends around a 12 feet long 2 by 2 (along the 16' edge). This will add some weight at the bottom. It will also make it easier for you to roll the bottom to ensure a better air flow.

I made my 2 by 2 from a 2 by 4 cut in half using a circular saw.

Put the whole plastic film over the greenhouse, center it and staple it to the vertical sides. Fasten the film with 1 by 2 boards on the frame and trim off the excess

You can see that in my case I used construction tape to create a plastic sheet long enough.

Step 6: Make a Door

Make a door to the dimension of the opening of the greenhouse. If the opening is 3 feet, make the door slightly larger (3' 3" for example).

You can use 1 by 2 spruce or pine to keep it lightweight. Some plywood in the corners will keep everything straight. You can also add the crossed wires we saw previously to prevent any movement over time.

I added a barrel latch on the outside and a simple hook on the inside. The door is screwed on the greenhouse using 2 hinges.

Step 7: Grow Vegetables

The configuration inside the greenhouse is up to you. I created a raise bed in the middle to keep the ground warm (the ground can be pretty cold in the Yukon). The 2 beams at the top are strong enough to hang growing baskets such as tomato plants.

The center of the greenhouse is quite high and can accommodate fast growing plants. The sides are better suited for herbs and lower vegetables.

Here is a list of plants I successfully grew in the greenhouse:

Mint
Basil
Oregano
French Tarragon
Rosemary
Cilantro
Various Peppers
Zucchini
English Cucumber
Various Strawberries
Parsley
Arugula
Tomatoes (Coeur de Boeuf, Coeur de Pigeon, Stupice, Sun Sugar)

Step 8: Ventilation

After a few months of use, I realized ventilation is crucial. Too much humidity creates mouldy conditions whereas too much heat prevents plant growth and makes some flower sterile.

I installed a 12V computer fan on top of the door and hooked it to an arduino using a temperature/humidity sensor and a 5V relay. A wifi shield sends data so that I can monitor the conditions inside the greenhouse while at work.

The system works fine but the fan is probably a bit small since the temperature decrease is minimal.

I used the DHT22 Sensor for its range of temperature and humidity.

The wifi shied is the CC3000 from Adafruit.

I followed the tutorial available on this page. However the Xively service is no longer free so you will have to find a similar service.

The electronics can be housed in a food container screwed on the inside of the greenhouse. I put mine beside the door, not far from the fan. The sensor should be placed in the shade at plants temperature to get a realistic reading.