If the OP is asking this question, then he probably has no idea what you're talking about.

Plastigage is the cheap and easy way to go. It works just fine if your not building some high horsepower track engine that you want to be 100% perfect, but I'd rather know my clearances regardless of the purpose of the engine.

Read up on Plastigage, and understand how it is used before using it. I'm sure it will do you just fine.