My first build was a 24" boys bike. The engine fit fine and the finished product ran well. But the frame was cramping my size of 5'10". My knees were only inches from the handlebar grips. I felt a little like a Shriner on one of their microbikes. Finding tires and little parts and pieces was never a serious problem. A lady friend found the high center of gravity compared to wheelbase made it really easy to fly over the handlebars if hitting a low curb and applying front brakes too hard both at the same time.
My 26" Haro V3 men's bike was much more agreeable. I rode it over 1300 miles. Am now moving on to additional 26" builds with 2.3" tires (I don't recall those tires available in 24 inch diameters).
MikeJ