Can you cut into the sheet rock at all? Preferably in a room that has a thick interior wall?

Say about 16-24" deep. The reason I ask is this. Studs are supposed to be placed about 16" apart. Many places skimp on this and it gets overlooked during inspection. To save money alot of builders will space their studs out further. I've seen some as far apart as 3ft.

Take a stud finder and locate a stud.. Drive a nail through it to verify that it is a stud. Then with a sheetrock knife cut out a section of sheet rock from stud to stud. You'll want this at least 2 ft high because you'll need to be able to get inside there a little bit to hook up your equipment.

Go to home depot and get the following.

Putty/spackle
Putty knife
2 hinges
2 magnetic latches
1 louvered circular vent
screws
nails
duct tape
sheet rock texture spray can.
a 6' 2"x2" cut into 3 2' sections

After cutting the square hole in your sheet rock take your 2' sections of 2"x2" and lay the edge of your sheet rock against it. With small nails tap the nails gently through the sheet rock and into the wood. Use the nails generously. Repeat this for the inside of the sheet rock on one of the sides where your hole was made. Take your 3rd 2"x2" and place it on the top part of the cut on the wall where the hole is at.

on the cut out sheet rock and on the side of the hole where you placed the 2x2's we'll attach hinges.. screw into the 2x2's.. get the pieces of sheet rock mated as close together as possible.

on the top part where you put a 2x2.. take your magnet latch and place one end on the 2x2 and one end on the sheet rock you cut out.. This will secure the sheetrock in place when the grow area is closed.

about 5-6ft up from the floor cut out a 4" circular hole and attach a louvered vent.. paint the inside of this vent and the ducting that will attach to it black.. This will hook up to your light system hopefully with a cool tube and a squirell cage fan or soething else that moves alot of air.

place duct tape over your hinges and everywhere you made a cut in the wall. Lay putty/spackle over the duct tape and allow it to dry.

Once dry spray the sheet rock texture aresol can over the duct tape.

Paint it to the same color as the wall.

This will provide you with stealth and cooling. The problem is finding an inside wall that's suitable to cut open. Closets and closer towards the boundaries are the house are generally good spots to find additional space in your walls.