Sorry for the delay: I can only attach 10 pics in each post and this specific forum needs approval first, so I couldn't reply to my first post until now.

This painting booth is complete by the way (this isn't a project), and I've been using it for a week now. Whew, sometimes it's more work to document, take pics, and post about this stuff than actually do it.
Here's the remaining guide and pics (in 2 posts). Thanks!
Assembly is a breeze with PVC if you're assembling something temporary because the pipes simply push into the connectors and hold with their own friction. If you want something more permanent, you can use PVC weld (a glue that melts PVC on the surface and bonds the melted parts together) or other glues.
Since I won't need this in my garage all the time, I can push the PVC parts together without glue so that I can disassemble it later for storage.
Here's some pics of the assembled joints using the 2
1/2" pipe sections...
Middle pipes meet and attach to the rear corner pipes with 'T' connectors:
Top corners meet with 'T' connectors, then continue with a 90 degree elbow to complete the top pipes:
The top middle pipe is what we'll use to hang
PC panels, and connects with both a 'T' and 90 degree elbow:
The final assembly looks clean and is roomy. I tried this first without the middle down pipe (used to support additional weight for hanging
PC panels), but later added the middle down pipe in pics you'll catch in my next post.