It depends on what you want it to do.
If you just want a very dry space so no nasty room reflection color the sound, a "tent" made out of PVC pipes and old drapes or moving blankets can work fine.
If you want something that looks more professional you can build walls of plywood on one side and tack/glue fabric on the other side, put hinges on and you have a portable and adjustible booth.
I'm sure there is lots of info in the "studio building" forum (see: below)
