^ i built a pretty similiar booth to 5ths a year and ahlf ago, from the pictures, but i ended up cutting some corners, and my sound really suffered.
its important if you are building something like this, to GET AS BIG A SPACe as you can to use. usually, the bigger booth the better the sound (up to a point.)
and you should foam, but DONT over foam. i would reccomend using the real foam or something like it, as it sounds like 5th did. i used some old foam sleeping mats and other shit, some of it like 3inches thick, and it just muffled the hell out of everything. not to mention the extreme proximity effect i was getting.
there are plenty of plans on the internet that i found when i was doing, i think if you google it youll come up with somethings.