It all depends on your place where you want to grow. You want to figure on how to get fresh air and to exhaust air. Can you place a tent near that? How are you for space? Which would be easy for you to do? tent or fixing up closet? There are different sizes of tent from 2'x2's to 10'x10' 2'x4', 3'x3'...i have a 2 in one tent. a 3'x3' for flower with a 1'x3' on end for veg and clones.
The tent will be noticeable...the closet can be not noticed. if that is a concern.
As junk said...with a tent it's pretty much all ready for you. Depending on the tent, some are not as light proof as others...so beware there. light leaks around poor stitching or the zipper area.
My tent is a cheapy, so it has those pin holes. but it is in a room i am able to keep dark. so no problems.