I am wanting to paint my room a grey/purple color but I want to put a top coat of glitter on top. How would I do this and make it look nice and even and not peel or rub off?

Top coat the glitter with a semi-gloss polyurethane. You could try mixing some glitter right in the poly to see if you can keep it stirred up enough to apply with a roller otherwise you'd have to apply the glitter to wet paint.

Why not just use a product like Benjamin Moore's Glitter Effect, you get your glitter and a protective top coat in one shot.
Benjamin Moore Glitter Effect