The answer to this question can be found in Chapter Two of this great novel. This, of course, occurs directly after the brutal murder of Susie by Mr. Harvey in his structure that he had built in the field. Let us consider how Susie's heaven is constructed:
When I first entered heaven I thought everyone saw what I saw. That in everyone's heaven there were soccer goalposts in the distance and lumbering women throwing shot put and javelin. That all the buildings were like suburban northeast high schools built in the 1960s. Large, squat buildings spread out on dismally landscaped sandy lots, with overhangs and open spaces to make them feel modern. My favourite part was how the coloured blocks were turquoise and orange, just like the blocks in Fairfax High.
Soon, Susie begins to realise as she spends more time in "her" heaven that actually you make your own "version" of heaven which reflects your own understanding of life and the world. The javelin throwers and shot putters are actually in their own heaven too, just like Suzie. Their "version" found a "fit" with Susie's heaven, and thus they were there too. Thus Susie's heaven features her own school buildings and even things such as the coloured blocks which are a direct copy of her own school.