Right now I am using Propane burners to keep the building warm. Is it cheaper to use electric heater or Propane (in genral). Any help will be appreciated.

Chickens do not need any heat whatsoever. Speaking from expericence in northern Michigan.

You will need to insulate the henhouse, the walls need to be a double board, with preferably closed cell foam, the upper "ceiling" with a fiberglass batt type and a wall vent in the corners that can be closed off for winter time. Plus a window or two of course.

The floor with plenty of small stone type gravel for the hens to scratch in and pick up badly needed small calcium stones and rocks.

The hens will develope sufficent feathers in the fall to do very well in winter time.