+1 to what ma3k said, ideally you'll want to get a GI or anywhere between 65-70", for riding in town, the gear inch calculator that tick.tick.tick posted is a good one and will show you different alternatives to get to the magic numbers, anything over that is a bit big, for a first timer, you'd get used to it, but it'd be difficult to spin and come winter it'll be much harder.
The only issue is whether you'll be riding using 700c tires or 650c, that will make a difference, but you can select tire size in the calculator as well..