I believe I’ve posted before on my technique for copying patterns for alteration purposes. Since then, I’ve found a better resource than FedExKinko’s for large format copying.
Look for your local blueprint copy house. The price quoted me at mine was about 60% cheaper than Kinko’s! 20 cents/square foot vs. 69 cents/sf.
The pros: You never have to worry about making alterations to the original or ruining it.
The cons: There’s a slight chance your original might be damaged in copying. I’ve had exactly one piece be mangled out of many, many pieces.