Sorry Brad, it is NOT plywood. MDF stands for Medium Density Fiber(board) It is like sawdust bound with a resin. VERY heavy, Very Smooth, and fairly cheap
If I were going to build a quick, down and dirty booth, the hell with frames. Lets get it done. You could build this in an afternoon, once you had all the materials, tools,hardware, and foam. All this has to do is keep room sounds out of the mic, right? This will do it. Ugly, but effective. So get busy!
Cut the ends off 4'x8' sheets of 3/4" thick MDF, so they reach from floor to ceiling with 1/4" clearance. Cut ONE panel 1/2" shorter than the height of the room. That is the door. This gives you 1/4" clearance at top and bottom.
Then cleat 3 panels together with 2x2's on the interior corners to form a 3 sided box IN PLACE. Cut 4 pieces of 2x2 cleat to fit between the corner cleats along the inside at the ceiling and fasten to the ceiling with drywall anchors. Just remember to predrill pilot holes in the 2x2.
Then screw one 2x2 alone each edge of the open end as a door jamb, and fasten another panel to one side with heavy duty hinges
as a door. Mount a cheap gate hook and it's a done deal. What the heck, your not doing anything fancy for isolation anyway, so why waste time with frames. The heck with ventilation, open the door

Line it with 2 layers of carpet foam backer, fastened to the inside with sprayon foam adhesive, or Acoustic foam tiles. Run some foam weatherproofing strips with peel off adhesive backer, up the edge of the door to seal it and VOILA! A down and dirty booth that you can simply unscrew and take with you!! Just predrill all the holes through the MDF, to fasten to the 2x2's. Use 2" drywall screws to fasten the whole thing together, but countersink the holes first. Mark off your screw holes at 6" on center up the edges where the corners come togeather, Consider the second panel the BACK. THE first and third the sides. Fit the back OVER the edges of the 2 sides. Actually, screw the 2 side panels to the 2x2 edge AND ceiling cleats while they are laying on the floor. Mark the outline of the 4x4 box on the ceiling. Fasten ONE piece of 2x2 to the ceiling where the back goes. Raise the back(make sure you have PRE DRILLED screw holes in the panel at both edges and the top) and fasten it to this cleat.
Then raise one side, fasten the back and the ceiling cleats. Then raise the other side and fasten it the same way. Then fasten the ceiling cleat for the DOOR. EASY. In fact, you could build a 2x4 frame for a floor, and cover it with a layer of MDF too. Then you have something to fasten the panels to at the bottom also, and that would provide a place for a seal for the door at the bottom too. Draw it out on paper and that will help you.
A little paint on the outside, and maybe if you feel like it, cut a hole in the door, screw a little 2x2 frame around it and pop some plex or 1/4" glass in for a window. EASY, just think about it for a while. Cutting MDF is easy with a skill saw, if you clamp a board across the end as a straight edge guide. Hell, one cut on each panel is all you need.

This stuff is HEAVY though, and hard to manuver in small spaces. But the MASS of the MDF is what will give it SOME, and I mean that with tounge in check, some isolation. But what the hell, like you said, you DON"T need real isolation.

But you DO need a booth, and this will make it quick, cheap, down and dirty and 4'x4'x8' tall.
Here is what you need.
(4)sheets 3/4"x4'x8' MDF. Even home depot carries this usually.
(6) 8' 2x2's A box of 2" drywall screws.
8 drywall anchors long enough to go through the 2x2's and the 1/2" sheetrock ceiling(2 per cleat)
128 sq feet of foam carpet pad(double that for 2 layers)
24 linear feet of foam weatherstripping( or use some scraps of the carpet
foam between the panel and the Jamb.
3 heavy duty butt hinges and 3/4" screws for each
1 SAFETY latch of some type on the INSIDE ONLY.(you do NOT want to get trapped in this, as you REALLY could die if you were alone
Optional floor and window
3 more 8' 2x2's (cut to fit whatever size window you want) You figure out how to frame it in, and HOLD it in. I would use 1"x1" wood stops if it were me.
1 more sheet of MDF
Glass or plexiglass cut to required size.
Good luck.
fitZ
PS. this is just a BIG BOX. Think in those terms and it becomes EASY.

But THINK ASSEMBLY SEQUENCE! Do all the hard stuff first, like predrilling holes, fastening hinges etc etc.