Best 2-car garage dimensions? (limited to 485 sqft)

[Tom A.]

We're building a spec house with a detached garage on a city lot. The garage can't be larger than 485 sqft which means we could build a garage 24w x 20d, 23w x 21d or 22w x 22d. Any thoughts on which would be most useful for the future homeowner? Since it's a spec house we don't know if it'll need to fit small cars or Suburbans.

20' deep seems tight to walk around with a fullsize SUV or pickup but since it's detached there's no issue with walking around the vehicle to get inside, just walk out the garage door or side man door. Depending on the width and depth it presents different limitations on storage of lawnmowers, bikes, shelving, workbench, etc.

Thoughts?