In the winter the angle of the sun is much lower
You probably will not see as much heat on the roof during that time
You would need something above the insulation & against the plywood to soak up heat
Either Alum or copper
Then a means of transferring that to the house
The problem is you would need this for each rafter bay
Much better of building a system outside that can be bigger
Do a search on the web for solar heating
I plan on building one like this
In the last pic that is 84.6 degree air coming out on a winter day
(not my setup)