The short but maybe embarassing method is to ask your customer what he wants / needs. The embarrassing part may be when he says "youre supposed to know that stuff - what do I need you for?
To answer your question you need to know what the load demand is ie current, voltage
and if motor start current and max overload current,
lenth of wire run, how many conductors in cable or conduit, ampbient temperature,
environment stuff like dry or in wet weather, if in a combustible atmosphere (gas, liquids, combustible dust etc)
I cannot think of what else I am forgetting.
You need to get copy of a good electrician handbook and the NEC since you are in USA and start studying.
Dan Bentller