You are right he was looking for a ratio but the concrete company does all that in their mix. At least he didn't ask about what slump and compression factors to use such as 3000# or higher and how runny or dry he wants it. Or if he wants fiber in it, size or rock, amount of cement, strength of rock, amount of water, amount of sand, etc. There is a lot to concrete mixes any more. It is either buy quikcrete or call for a truck. He just needs to call one or more of the concrete companies in town, tell them he's bidding a job later this winter, ask them about the concrete, and get a price. He may just want a partial load under a certain amount(like a yard) and then they charge extra. After hand mixing 8 bags the other day, I probably would rather pay extra to get any more than that trucked. But he also has to worry about location where he may have to wheelbarrow it in or build a chute through a window.
If he is mixing his own or using quikcrete, then he shouldn't worry about adding anything else. By the way, that quikcrete book is a handy reference that tells you how to make about anything including brick and block walls, repairing stucco, etc. The pictures and drawings in it are for guys like me. It just forgets to tell how hard it is to mix a bunch of bags of quikcrete by hand for that big patio.