Looking at the size of the building to both the car (automobile) and the bulkhead flat car i would say that it is N gauge. The flat car has got to run out at around 50 feet in length so you would indeed be able to fit a small branch of pizza hut onto it.
As for the comment above re: pizza mansion, LMAO
but it's true, some of the branches of Pizza Hut over here are comparable in size to maybe a 40 seat diner. But as suggested the size of the door will be the telling factor, should be in the region of 15mm high by 6/7mm wide (approx).