Perfect room size...

my converted garage almost identical dimensions sounds very good with a little treatment roomtunes products called corner tunes and Echo tunes cure the slap Echo you may have and room len's fine tune your sound stage.

Sorry, I was getting tired last night. I didn't mean that speakers should be moved around for reverb (a function of surface area, surface type and room volume). I meant reflection time adjustments (back wall, side wall, etc. from the speakers to the listener).
By the way, you may also want to do some research on past threads (acoustics, room treatments ...) to see what people have said -- e.g., how walls should be constructed.
Have fun!

The ideal is far from noncontroversial, unlike what several comments above suggest. Just work out the main resonant modes for various dimensions: the "golden ratio" is good but not obviously (or really) better than some other choices. I recommend (once again) F. Alton Everest's books, "Sound Studio Construction on a Budget" and "The Master Handbook of Acoustics, 4th edition", to learn how to analyze a room's acoustics. In "Sound Studio" he proposes a set of room dimensions that differ from "golden ratio" ones, and tells you why they're good, while granting that others can be good too. This book has many other worthwhile features as well, and no one planning a listening room should fail to read it, IMHO.

Thanks to all of you for this good advice. Any other suggestions will be welcome.

will