Don't know if I'll jump in or not.
Granth, if you go the black pipe route, most of the Home Depots will cut it into the lengths that you want when you buy it in the ten foot sections. Also most (at least around me) don't charge for the cutting. They only cut 90 degrees, no angles. So try to figure out what lengths you'll need and let them do it. It does save time and gives you good straight edges to start with.
Also the Home Depot guys will cut conduit if you ask nicely on the same pipe cutting machine ( in my area anyways). I'm 300 pounds and I've ridden sevral bikes made outta conduit. If you stay with 1 1/2 inch or bigger and don't get crazy with your riding, the conduit will hold up.
One other thing, let them know you're building a bike out of it. I've gotten scrap pieces up to two feet for free from our guys!
No matter what you use to build your frame, make sure your welds are strong! When in doubt use gussets.
I'll be watching this thread and who knows .......