Need more roosting real estate

Our little coop only has a 6' roost. At this point we have 12 chickens. We are only keeping 6 but haven't decided which 6 yet so we will have them for a little while longer. In the meantime there just isn't enough roost space. We are planning to put in new nest boxes (because the current ones are too small at about 9" square) and the current ones have a shelf in front of them so I'm thinking about opening that up and let them roost there (in addition to the other roost). The current nest boxes will be closed off but is it ok for them to roost on a shelf (it has long strips cut out of it)? Otherwise there isn't really room to add a 2nd roost. The coop is only 4 x 6 and only about 4' tall at the sides.

When we add the new nest boxes they'll be down toward the bottom where the current roost is and there will be a board over them to avoid poop getting on them. The current nest boxes are across from the roost but there are a lot of studs on that side which is why we want to put the new ones in the other side.

btw this is a prefab coop. If I had my way we would have built one and it would have been bigger than this and tall enough to stand up in. Didn't get my way.