List of Stuff: Table Top / Lumber / Brackets / Stain / Stain Applicator (T-Shirt Rags) / Latex Gloves / Sandpaper / Steel Wool / Hammer + Nails (Optional) / Beer
Step 1: Buy a Table Top
Note: I didn't do this step first and it made the project harder. Once you have your table top, coming up with the dimensions for your other pieces will be much easier!
Step 2: Buy Some Lumber
What kind of wood: A few 2x4s should do you (I bought three at 12' which made for 8 legs, 2 braces, and some extras). Note: Having extra pieces is good in case you screw up. Don't worry about what kind of lumber but Don't Buy Treated Wood. If you're like most people, you'll probably be working at your desk indoors, so there's no need to buy weather-treated wood.
How to get your wood cut: Most hardware stores (Home Depot, Lowes, Ace) have a saw to cut your lumber for you. Just grab the nearest employee and ask if they can operate it for you. Or if you're like me, stand by it until someone takes pity on you. Once you find a saw operator, there going to ask you what length you want the pieces cut. For my desk, I had the legs cut at 19'' and the braces cut at around 23". If you think 18.75" and 22' seems better, by all means. Just remember that the sawhorse brackets will add a few inches in height.
All in all if you do this on the cheap without buying the premium lumber, this step should only run you around $20.
Step 3: Buy Sawhorse Brackets
Step 4: Buy Wood Stain + Other Stuff
Other Stuff: Fine Sandpaper / Gloves / T-Shirt Rags / Steel Wool.
Note: If you have old t-shirts around, go ahead and rip them up and use them. Most people prefer white t-shirts because its easier to gauge how much stain is on the rag.
Step 5: Get Sandin'
You'll want pay particular attention to the ends. Sanding them down will make it easier for them to slip into the brackets and it lessnes the chance you'll get stuck by a splinter. Once your done, wipe off any excess dust.
Step 6: Get Stainin'
Depending on how dark you want the desk to look, you'll want to apply at least two coats. Make sure you block off a good amount of time for this step. After you apply a coat, not only will you want to wipe off any excess stain a few minutes after its applied, but you'll want to let each piece sit and dry for an hour or so. Once they're dry, take your steel wool and lightly scuff each piece. This allows for more stain to penetrate the wood on your next coat.
Note: When wiping excess stain, be sure to go with the grain of the wood. But if you don't, its not a big deal. There will be some streaks but the desk shouldn't look perfect.
Step 7: Assemble!
Disclaimer: You'll notice that each bracket has holes for nails. You don't need nails. Other people have made perfectly fine sawhorse desks without them. But In my opinion, nailing the brackets in makes the desk feel much sturdier. If you decide to get a hammer and nails, use your best judgement. Standard, 16-penny nails and a small hammer should do the job. Also, try to make sure you're setting your table up on level ground.
When the sawhorses are done, set the table top ... on top.
Step 8: You're Done!
Be proud. At this point, you should feel pretty good. If not, sorry. For you happy people, enjoy a celebratory beverage as you pat your handy-self on the back and examine your work.