CVORnurse - A tape measure can tell you, or maybe a look from above from your attic. Don't forget to account for wall thicknesses. Typically 4.5". My dad has about 6" between his bathroom and behind a built in desk, but it's not very usable except as a wire run area for aux lighting. You might could store some guns in there if you can build an access door.
My dad frames custom homes and he has put in hidden rooms before. I'll have to ask him how they hid the opening. It wouldn't be too hard to hide a door in the back of a cedar lined closet. Wood paneling could work as well. I think sheetrock wouldn't be solid enough to work with and hold up to long term use.
Power outlets, a small night light, and insulation for sound deadening would be nice.
My dad frames custom homes and he has put in hidden rooms before. I'll have to ask him how they hid the opening. It wouldn't be too hard to hide a door in the back of a cedar lined closet. Wood paneling could work as well. I think sheetrock wouldn't be solid enough to work with and hold up to long term use.
Power outlets, a small night light, and insulation for sound deadening would be nice.