My coop build

[LanceTN]

It is the garage and there is no need to get back there. Only about a foot of room between the coop and garage. Plan on putting a gutter possibly use the water off of the roof for the chickens.

I am now worried about the osb and moisture from underneath even though it is raised 2 feet off of the ground.

I'll do 2 roosts first 1 foot from wall and the second 1 foot from that. Both being about 2 feet off the floor. Use 2x4s or are 2x3s wide enough?

I'll also put the nests 1.5 feet up to keep them off the floor

As long as you allow air flow underneath you'll be fine. Trapped moisture rots wood, so don't trap it.