DYI diffuser kits/plans

Hello,

I am long overdue for room treatments. Does anyone know of any plans for creating diffusers and/or absorbers? I have searched the archives and did not see anything. I have also checked other sites. The kits that you can buy seem to be about $100 for a 24X24 panel (diffuser). I am hoping to make my own. Also, Room Tunes, is it possible to build something like these?

Thanks, Paul