Hi Alizar19,
the roof structures that you created (building=roof) are meant for buildings that have no sidewalls and have only a roof. For example covered gas stations. see. https://wiki.openstreetmap.org/wiki/Tag:building%3Droof

I assume you wanted to draw different parts of this school building. For that you have to use building parts tagged as 'building:part=yes'. See this wiki page for more details. 
https://wiki.openstreetmap.org/wiki/Key:building:part