Next day you can prime the whole thing. I started from the inside and did the outside last. I primed every surface as I intended to paint it all. By painting it all black inside, you eliminate the chance of seeing through gaps in your cabinet and seeing bright, unaltered plywood. It’s your call as to whether you want to mess with it.
The plywood piece for the back that you created several steps ago should be primed and painted also. I just put it across the two saw horses (see picture 3) and did the interior side first. The reason I did not install it yet will become obvious when you start to paint the interior- it makes it a lot easier to paint from the back side without it in place.
I applied both the primer and paint with foam brushes, 3" rollers, and an 8" roller for the sides. The rollers made quick work of the large areas. I let the primer sit about an hour before applying my first coat of paint. I was quite anxious to get it painted as well as clear the garage so I could move the cars back indoors. It was winter.
Inside areas got one coat while I put on two generous ones on the outside and the back panel. The first two pictures show one coat all over. You can definitely see areas that were missed in these two. However, it will never be noticed due to these areas being enclosed within the cabinet. The goal is to get color inside so if there are any gaps in your construction, you won't be able to see anything that will detract from the gaming experience. Be sure to also lightly hit the edges, where the T-molding will go but no so much that paint gets into the slot. A toothpick works if some paint does find the crevice.
The second coat made all the difference. Two coats made it look very nice. The photos don’t do the cabinet justice. Black doesn’t photograph well. I ended up using a third coat on the sides just because it wasn't entirely perfect after two. As I said before, no one except the builder will ever notice these slight imperfections (read: character).
Let it sit over night. The next day you can attach the back panel. Just push it up tight against the top of the cabinet and screw in four screws at the edges. I left the screws exposed so I could easily remove the back if needed.
After that you can take it inside for T-molding installation and the all important testing.
