I built my new garage 24x28, based on four foot increments, sized to keep the cost down too. Eight foot walls on top of two rows of 8" block along with scissor trusses gives it a taller big open feeling. But also 28 foot deep to at least allow for a fishing boat on a trailer in the garage, with some room behind it. Same for a snowmobile trailer or ATV trailer. None of those for me as this is my motorcycle shop garage. But I figure a slightly deeper garage is more marketable. For someone with cycles a person could park two cars in it, and sill have room to the side and in back for a workbench or cycle/ATV/lawn tractor-ZTR lift.
Someone could even install a two or four post lift in the center. With my Dakota pickup on a lift just below the ceiling would still provide almost six feet clear under the truck.
I'm no architect, but I have always been aware of size and proportions. A 24x24 garage will look like a box, unless some detail is added to the roof, as in overhangs, pitch, etc. I designed my 24x28 garage with a hip at each end, and the front hip includes a small gable detail with a small center peak over a small window. From the street it adds a lot of visual appeal. But also, since the garage is only 24' wide but with almost 10' high walls, a simple gable front with a low pitch would be odd looking to me. So I added a bit more roof pitch and front gable detail to break up the vertical aspect.