Two great links, BTW - I've spent a lot of time on both. Also if you are interested in this kind of thing, get yourself a copy of The Master Handbook of Acoustics
by F. Alton Everest - more than you'll ever need to know.
the walls should not be exactly parralel etc. These things does not cost extra.
Ever try to get a builder to build a straight
wall, let alone an angled one? ;D RFZ rooms are a great design, but difficult to build properly
. They also have a very narrow "sweet spot", so they are rarely used for small one room studios. A rectangular room with the proper treatment works better for a single room studio - like a LEDE design.