What is your climate like? Heating for chickens is very dangerous, and unless you get below -10 in the winter I would not provide heating.And then I’m assuming it’s gonna be a heck of a lot easier to heat it in the winter time because the peak is so high I can put a heater in there now here’s one question do I put the roost higher than the nesting boxes? I’m assuming yes so should the nesting boxes be on the ground or elevated up a little bit? And then do I need to put in flooring which is fine because there’s no floor attached In the house
Roosts go higher than the nest boxes to keep the chickens from sleeping in the nest boxes.
No floor is OK, as long as you have a good thick litter on the floor.
Because your play house is 3.5x4 I would try to make the nest boxes external if you could.