Sweater Design in Plain English was published in 1990. In it, Maggie Righetti uses examples and simple formulas to help you calculate the measurements you need to make your set in sleeves fit, as well as calculations for chest width, length, shoulder slope, neckline, etc. In short, everything you need to design a sweater to your own specifications.
As given in her examples, Righetti's ideas of design and fit don't jibe with mine. Her design aesthetic seems dated. But that doesn't matter. With this book you get the tools you need to do it your own way.
So I designed my armscye and sleeves based on Righetti's advice. I haven't finished the sweater yet. I'll let you know how it comes out. But along the way I found two incredible Internet resources. Lucia, the Knitting Fiend, on whom I have a knitter's crush, has made a sleeve cap calculator. Check it out. And while you are there check out the endless number of calculators, tips, techniques, patterns, and how to's that Lucia provides out of the kindness of her heart.
The invaluable Jenna Wilson, through the wonder of Knitty, has also published a series called "Ravellings on the Knitted Sleeve" which includes a wonderful article on sleeve types, and a fabulous primer on creating a set in sleeve.