An easy way to estimate how much a stack of plywood will weigh is to figure about 25 lbs. per 1/4 in. of thickness. For example, one 4x8-ft. sheet of 1/4-in. plywood will weigh about 25 lbs., 1/2-in. about 50 lbs., and 3/4-in. about 75 lbs. This can help you decide how many trips you need to make to get a stack home, or whether you should have it delivered.
Attic doors are a major source of heat loss in many homes. To stop airflow, weatherstrip the edges and insulate the back side of the attic door. Fold-down stairs can be covered with a lightweight box made of rigid insulation.