We always recommend that a qualified roofer or builder install skylights, however you may wish to determine the size you want. Selecting units that fit between the roof trusses will reduce the amount of labour required for installation.
Calculate one square foot of skylight for every 20 square feet of floor space. Choose one large skylight or several smaller units to achieve the effect you want. For Example: Your room is 12’ x 12’, or 144 sq. ft. Divide by 20 sq. ft. of floor space and you will need 7.2 sq. ft. of skylight.