That's kinda weird and never thought it will happen only maybe in Shuwaikh Industrial Area shops, but not in my area !I really don't understand the reason of putting the red car on the top of the house. Is it some kind of a decoration ? they're turning their house into a shop ?
As they say in Arabic " اذا عرف السبب بطل العجب " or if you knew the reason you'll wonder no longer.