How Do I Build a Four-Sided Cupola?

Calculate the angle of your roof ridge. Run a tape measure 3 feet out from the top of the ridge, using a level to ensure a true horizontal. At the 3-foot mark, run the tape measure straight down to the roof. If that distance is also 3 feet, you can use 45-degree angles. If it's 1 1/2 feet, you can use 30-degree angles.

Cut your 2-by-6 lumber into four equal boards. Sand the wood and then angle the ends of two of them using a miter box to match the angle you found in Step 1. These boards will be the base of your cupola.

Cut your 2-by-2 lumber into four equal pieces to make a square for the sill. Cover the sill with flashing, using the tar to hold it secure. Then, attach the base to the roof with L-brackets. Use the carpenter's square to ensure that you have all right angles. Apply roof tar to the points where the base meets the roof.

Attach the louvered vents to the base using the hardware in the kit provided -- this will typically involve small brackets on the bottom of the vents, through which you'll run screws into the base. Mount the sill on the top of the vents with the same hardware.

Measure the length of each side of your sill square. Cut four right triangles out of the plywood, with the side opposite the right angle the same length as the sides of the sill square. Place one bracket on the left-hand shorter side of each triangle. Use wood glue to connect the triangles to the sill sides, and then run screws through the brackets to attach the triangles to one another, taking care to make the sides flush. Caulk all meeting points.