I’m in a similar situation, and my last grow was in an unused bathroom with a lock on the door. I began my current grow by purchasing a roll of 100% light proof (supposedly) window film and using it as wallpaper. The stuff is made by Vivosun who are also the manufacturers of the 96 x 48 x 80 grow tent that I just sent for (!) and comes in a roll a hundred feet long by a fraction over four feet wide. It calls it 48" by 100’, but I think they make it a tad wider so it can be trimmed.
A 100’ roll is around $30.oo (US)
I can’t really tell if the angled roof in your closet is flat, or if it has “Popcorn Texture” on it. If it is flat, you may be able to use the material I sent for and some silicon adhesive to stick up the mirror film. I goes pretty quick, since the silicon glue is enough to support the weight of the reflective film even when it is wet - NO STAPLES required. You put a line of dots of glue (best to get it in a caulk gun tube) all around the area where one sheet is going to go, and then spread it flat with your fingers. A wet cloth is best to wipe it off your fingers, because anything made to repel water will not stick to anything wet. I use a thing bead all around the edges and then some dots all in the middle part to make sure it doesn’t belly out from the edges.
By overlapping the edges with a solid glue bead, the room can also be made water and smell tight, on the floor or carpet you can get a ten-pack of cheap mylar emergency blankets (space blankets?) and just lay them down over carpet or whatever. if they get trashed, so what? Toss the ripped one(s) and unfold & lay down another. This also guards from spills and leakage
I suppose you could use wallpaper glue, but I wanted to be able to pull down the stuff later if I had to, and silicon sealer releases without damaging walls, in fact it can be peeled right off pretty easy, yet still has plenty of holding power.
The reason I sent for a grow tent is because I wanted to use the room for other plants that I am very happy and proud with/of and also because I wanted to concentrate the light being used for my “special” plants, rather than having them share what is really a pretty large room - about a 16 x 12.
I too am a vet, and I heard a rumble about Congress quietly passing a federal law in favor of medical pot, but I have no confirmation on that at this time
Be funny as all get out if the VA in my state gave out “Prescriptions” for MJ before the state itself pulled its collective heads out of their backside, now wouldn’t it?
~Frankie