You might be better going for 3 legs/feet rather than 4. It's diffucult to get 4 feet to sit on an even surface but 3 feet is no problem. Jut have 1 short leg at the back then 2 long ones at the front (think of a clock, rear at 12m front at 4 and . That way all the weight will be over the front legs and the back will keep it stable.
Good luck with it, post a pic if you get it built.

 Just buy the one I got, it sits snuggly in the corner when not it use, and holds 50 lbs. DH bikes with no problems!

See here in my album:
http://www.pinkbike.com/photo/1844171/

and heres a pic. of one set-up:
http://www.cyclestore.co.uk/images/products/Xtra/7031.jpg

 Sorry Geoff, but the pvc might be waaayy to flexy. Get a nice stiff, strong stand..

 i think it will work but the pins have to go all the way through ane you have to ballance the weight with something.