This Instructable will serve as hopefully 3 different things. 1) an example of modifying your intend build to suit the space you have, 2)Show you many good tricks for what not to do when working with wood, and 3) the aforementioned practice at making Instructables. Shall we proceed?
Step 1: Tools and Materials
1 8' x 4' sheet of 23/32 interior grade plywood
1 4" x 4" x 6' board
2 3" x 3" x 4' finished table legs
1 box of decking screws (I like decking screws cause they're so darn versaitle and hold up well for outdoor projects. Since you'll definitely have some left over might as well have something you can use later)
1 2" x 4" (you won't need much so some scrap wood will do)
1 8' strip edge moulding
Wood stain & Brushes
Polyurethane & more brushes
440 Grit Sandpaper
A Circular Saw
w/ assorted drill bits & screw driver bits
Wood working triangle
Safety glasses & gloves
A small putty knife
Step 2: Figuring Out Just What You Have to Work With...
I chose a corner piece design as it made the most sense given what I had to work with, and as you can see from the pattern below, instead of making it just a triangle I brought the sides out 13" to give me a bit more space to work with. I was also thinking about attaching a 13" shelf to one side but after I put the desk in I realized I didn't really need the extra storage.
Once you have all your measurements and are sure you'll be happy with what you're going to produce it's time to get to cutting...
Step 3: Time to Cut the Wood...
For the desk surface I used an 8' by 4' sheet of 23/32's interior plywood from Lowe's. The interior stuff if nicer and will cost more but as a desk surface it's worth it. An 8' x 4' sheet of plywood is big but I don't recommend cutting it in half before you start as you may want a nice 8' long section for something else later.
Important wood working tip #1
Interior plywood has 2 sides... ok technically it has 6 sides but you know what I meant. Anyway interior plywood has 2 sides, a really nicely finished side and a slightly rougher side. When you begin to trace out your pattern for cutting on the rougher of the two sides. When you cut you will be cutting on the rough side of the plywood. That way when your saw jumps like mine did and you leave a 2 foot gouge down the wood, it's on the rougher underside of the desk and not the top where it will need to be sanded out. I also cut a 2" hole in the back of the desk to allow me to pass cables through for my monitor, keyboard, mouse, etc. You'll want to do this before staining and sand around the hole afterward to clean up the wood surface.
For the legs I realized that 2x4 would be to skinny and make the desk prone to wobbling, 4x4 would be overly large and just look tacky. Makes sense that 3x3 would be an ideal size right? Well it is but you won't find 3x3 in the lumber section of most hardware stores. But if you go looking in the section where they have finished tables legs and small table kits you'll find them. They look great but they're not exactly cheap, anywhere from $13 to $25 per 3' section. Multiply that by 3 or 4 table legs and your desk just got mighty expensive.
Important wood working tip #2
Sadly I do not have a really nice, table mounted circular saw, I was doing everything by hand, if you are in the same boat as I make sure your cuts on the table legs are as level as possible. Hard to do by hand I know but if they're not level your table will wobble when you're all done. If you're putting this desk in a carpeted room you'll get a bit of forgiveness by setting the un-level side down towards the floor instead of against the wood of the desk, but only a little forgiveness.
Once you have the top of your desk cut out, measure the final product and cut to length 3 pieces of moulding to go along the 3 front facing edges of the desk. This will add a nice look and keep you from scraping against the raw edge of the wood.
Important wood working tip #3
Make sure you label on the back side each piece of moulding and which part of the desk it attaches to. That way you don't accidentally put the wrong piece of moulding on the wrong part of the desk.
Even more important wood working tip
Before you go to attach the moulding you might want to actually bother to look at the markings you made on it. Unlike I who true moronic fashion attached all 3 pieces of moulding (which I did mark ahead of time) without bothering to look at them and only afterwards realized that one side was cut just a hair short and one was cut just a hair long.
It may be kind of hard to see in the second picture but the moulding doesn't quite go all the way to the end of the desk. DOH
Don't attach the moulding to the desk yet though, we have a few more things to do first.
Use your triangle and circular saw to cut off several triangles from your scrap 2" x 4" (at least 4 total). We'll use these to keep the legs of the desk stable later on.
Step 4: And Now We Shall Stain...
Anyway, I wanted to use a wood stain as opposed to a paint as it would allow me to keep some of the natural wood grain in the desk. Now if you've never worked with stain before it's a lot thinner than paint and you'll probably find that you need to do 2 or more coats to get the desired color. For me I had to do 3 coats of black before it looks quite right.
Stain your desk surface (and edges), legs and the moulding before you attach it to the desk to make sure you get everything and don't have any of the natural wood coloring peaking out.
As you can see in the picture here I did stain the front two legs but not the rear leg as it sat so far back on the desk I saw no real reason to do so as it was a lot of extra work for something I'd never see.
Important wood working tip #4
When staining remember to lightly sand between each coat to take out any grit or particulate matter that was suspended in the stain, you desk will be much nicer for it.
Step 5: Time to Play With More Powertools
We'll be using our decking screws to attach the legs of the desk. Lay your desk surface upside down on a clean work space and start with the rear 4" x 4". Get it's position where you want it at the rear of the desk and using your hand drill attach 2 of the wooden triangles to the leg to hold it in place.
Important wood working tip #5
Don't forget to drill your pilot holes before trying to put the screws into the wood.
After the triangles are secured on the first leg, carefully turn the desk over and use your drill to make 3 pilot holes from the top of the desk straight down into the 4" x 4". Then drive 3 screws through the top of the desk, into the first leg. It's very important to remember to countersink these screws on the top of the desk.
Repeat the above step for the two front legs (using 1 of the wooden triangles this time), checking their position before you secure them to make sure the desk doesn't wobble.
There ya go, you're about 85% finished now, just a bit left to go.
Step 6: Cleaning Up the Desk...
Now we clean up those deck screws. Since you countersunk them like good little builders we can use wood putty to fill in the hole they made and use our putty knife to make it flush with the surface of the desk. Give this a day or so and we can do a final stain coat to cover up the putty. Take your time with this and no one will ever know there were holes in the surface of the desk.
Once all your wood stain is dry slap on 2 coats of polyurethane (remembering to sand in between) so that any tasty cold beverages, you place on your new desk don't stain it in the bad way.