I would convert each leg into an implied probability, then multiply all those together to get a probability for the entire parlay. Compare that to the implied probability of the offered price of the parlay to see the book edge.
This calculator is handy for quickly converting to implied probability:
"The Logic of Sports Betting" has a section on how to calculate this. I posted a link to the PDF version of the book here. It's in Part I, page 28 of the PDF.