your dad was right, an air pocket between walls is the best way to go, and most big studios don't go throwing foam all over the place because they have constructed floating-walls that provide the afformentioned air pocket.
what i'm telling you is stuff that i've seen done in other studios and what i've read in recording magazine. i've putting foam in my control room to deaden some of the reflections, but my room (since it has no height, width, or length multiples) isn't in horrible acoustic shape.
putting up the wood frame and attaching the 'soundboard' wood to that will create an air pocket (not a true pocket since your frame wood will be attached to both your normal walls and your soundboard wood.
then, once you've got your soundboard wood up. put up your acoustic foam such that it gives your mixing position (the triangle between your monitor speakers and your head) the most depth.
take a look at the primacoustic web page (
www.primacoustic.com) it has great stuff on it as far as where to put the foam even if you don't want their particular product (i just got it).
you need ultra thick foam (bass traps) for the corners of your room to control the bass boom, and 3" foam to help with the standing waves that make your room sound uneven.
i helped some friends who own a mid-sized recording studio in DC construct a pretty nice vocal booth and mixing room. stuff that i can not do here in my house (it's too small) was quite a kick to do in their studio.