I salvaged all the wood in this project, but screwed up the concrete bit, twice, so that cost a little bit. Between screws, polyurethane, and concrete, it should run about seventy or eighty bucks.
You will need these materials:
An old panel door, preferably solid wood
4 3'-4' pieces of 2" x 6"
6 24" pieces of 2" x 4"
40-60 lbs of thin-set anchoring/expansion cement
1" drywall screws
3" drywall screws
You will need these tools:
Grinder (optional for polishing concrete or grinding down if you over-fill)
First five photos by Mr. RaMell Ross (http://www.ramellross.com)
Step 1: Legs!
My legs were salvaged rafter tails from a demolition project, so they'd already been cut to a taper. If starting from scratch, cut up some 2" x 6"s to about 45", then split them diagonally with a circular saw, bandsaw, or jigsaw.
Then lay them on the door from your attachment point out to the corners of the door and strike a line on the under side of the door. Now you've created a triangle from the 1/4 centerline out to the corners of the door. Measure the angle of the point of the triangle and use that to cut two triangles out of scrap 2" x 6". These will become the attachment points for the legs. Screw and glue them to the door from the top, pre-drilling with an 1/8" bit to prevent splitting.
Hold a leg up to the triangle with the other end in the air and adjust until the foot seems to be roughly in line with the corner of the table. You might need a helper on this. Strike a line on the leg to get the miter where the leg meets the table. Cut all your legs to this angle. Screw and glue the legs to the attachment triangles with 3" screws, pre-drilling to prevent splitting.
Do the same with the leg braces -- just hold up a scrap of 2" x 4" and scribe the rough miters, then cut one and trace it onto the other four. The legs will still be pretty flexible and wobbly at this point, so push and pull them as needed to make them line up with the corners of the table. Toe-screw and glue the braces in with 3" screws, pre-drilling to prevent splitting.
Step 2: More Leg Stuff . . .
Next, to brace the legs off of one another, miter a 2" x 4" to fit between each pair of legs where the other braces come in and screw and glue it into place. The leg structure should now be extremely sturdy, without a trace of play.
Step 3: Concrete Prep
Sand down the door with an orbital sander, rounding off the edges of the door and legs well.
Set the table up on a level surface, shimming the legs as necessary to get the top as level as possible in both directions.
Step 4: Pourin'
However, it cures in 15-30 minutes depending on temperature and humidity, making it somewhat difficult to work with. I ended up over-filling my depressions, which led to me having to grind it down later, which cracked it a little. To prevent this, have a screed, or a piece of wood you can use to scrape the concrete level with the wood, handy. Also make sure you have enough -- the depressions seem shallow, but my door ate up 70 lbs of concrete. The product I used can be found here: http://www.quikrete.com/ProductLines/AnchoringCement.asp
Expansion cement is also self-leveling if you mix it slightly liquidy, which is why I suggested you level the table with shims under the feet.
So, mix up the concrete in batches in a bucket, wet but not soupy, and then pour it in. If you over-fill, screed it off, and be quick about it, because that stuff will set up on you in a minute.
Let cure overnight.
Step 5: Finishin'
Wipe down the table with a damp rag and then polyurethane the whole thing, concrete included. Once it was dry, I also lay two coats of wax on the top to protect the finish and prevent rings from cups.