Okay, someone asked on another thread what I'm reading now to prepare for our upcoming 21 Day Best of Europe tour. I'm about 2/3 of the way through Ross King's "Michelangelo and the Pope's Ceiling," which is, of course, about the painting of the vault of the Sistine Chapel.
I am enjoying it, and appreciate that it covers much more than just the design etc. of the ceiling. King's explanation of how and why frescoes work is wonderful. He actually describes the chemical reaction that results in paintings that last for centuries, and in some cases, even millennia. He also describes in detail exactly how the process is done.
But it's not at all a technical book. It's highly readable, with lots of interesting background on Michelangelo and his family, Julius II and his battles, and other prominent artists and architects of the time, especially Bramante and Rafael. There's even a funny anecdote about Martin Luther's visit to Rome at that same time.
King manages to put the Sistine Chapel and Michelangelo in an interesting social, cultural, and historical context. I recommend it.
He is also the author of "Brunelleschi's Dome," about the Florence Duomo. I guess I'm going to have to add that one to my list.