Its not bad at all.
Similar in construction to my home studio's vocal booth, except I have mine over a stairwell so the floor flips up so the stairs can be used occasionally.
I used 2x4 douglass fir as verticals, and floor sills. Caulked everything real good, then applied 2 layers of 1" MDF on the outside of the frame, in the studio.
On the inside, between the studs I installed another two 1" MDF. Not on top of the studs, between the studs. The walls are essentually 4" thick, with each piece of wood (stud or panel) chaulked heavily before being screwed down.
On top of that, inside the vocal booth, I have two layers of carpet (between the studs, which brought the surface of the panels between the studs to the same level of the studs), then attached greenboard (green sheetrock) on all surfaces to make for a smooth finish, then 3" auralex foam on top of that. Didn't need bass traps in the vocal booth, so I have spares.
My vocal booth is just large enough to fit a 6'3" tall person with a few inches above their head before they hit the foam, not idea, but I'm not that tall and the singer I often collaborate with is 5'3".
Track lighting on a dimmer around the perimeter, facing the walls, keeps the heat off the singer's face and throat. One one wall is a double duplex outlet for guitar amps and such, as well as a seperate set of junction blocks with midi, TRS 1/4", and XLR microphone connections, four of each.
I also got a little creative and mounted a JL Cooper Cuepoint on the wall - just in case *I'm* in there pretending to be a guitar player, I can "rock the reels" remotely.