Hi,
The multipolygon relation is not 'correct'. The role 'inner' cannot touch a role 'outer'. 

To me it looks like the red roof is one building ... then the other structure is ??? For the moment I have used the same tags on both, building=school, building:levels=2

You can check the osmwiki to see how tags are used - see https://wiki.openstreetmap.org/wiki/Relation:multipolygon