Wheels are 2 different widths, is this a problem?
 

I have a pair of wheels on my new build (first build) with 2 different widths. Both are 700c's, but the rear measures 20c outside, 14c inside....the front measures about 26c outside, 20c inside. It will be a while before this hits the road. (I'm still in a sling for 4 more weeks) I'm wondering if the difference in size will effect the ride? Also, when tire size is considered, which measurement dictates what size tire will fit?

It probably won't affect the handling but you are going to have some problems with fitting a tire narrower than a 25mm on the front rim. Even a 25mm might look a little odd with the wide front. A 32 to 37mm tire might be more appropriate for that wide of a rim. If the fork is of a low form, the tire might not fit without rubbing.

Shouldn't be too much of a problem. There will be a slight handling difference in the turn-in transition due to the difference in profile radius of two identical tyres mounted on the different rims, but doubt most people would ever notice it.