If you want to build one, cut the pipe into 2, two foot sections and the rest into one foot sections. You need 4 elbows and 2 "T"s from the "big box" plumbing store. Glue everything together except for the 2 upright portions of pipe. I used some woven string from an old venetian blind to tie the uprights to the frame to keep them from getting lost. Leaving the uprights unglued makes them easier to store, stack and transport.
The wooden uprights are cut from 1 cheap 2X2, both 4 foot long. I used a rasp to round off the portion that fits into the upright pipes.
Now I just need some cardboard to staple to the uprights and I am ready to go shooting! Make some for yourself if you think they might work at your shooting spot.