During a vacation to Italy several years ago, I was impressed by the intricate vaulted and domed ceilings in the churches of Rome, particularly the coffered dome of the Pantheon, built by the Romans around 126 A.D. I figured if the ancient Romans could build such a spectacular structure with the simple tools of their time, then I could too. So, back home, I decided to build a domed ceiling with elliptical rafters in the center of a 16-foot-by-25-foot family-room addition to my own home.

I would have preferred a deeper dome but didn’t have room overhead: Because the addition — an ell off the back of the house — was only 16 feet wide, I was limited to a roof pitch of 6/12. I settled on a diameter of 9 feet and a height of 2 feet measured from the bottom of the ceiling joists to the bottom of the collar ties.

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