Hi jotoga, Thank you for contributing to OpenStreetMap (India).

You have added a few buildings which are overlapping with each other. Please try your best to avoid any overlapping building polygon.
Please remember to square the building for squared buildings (the shortcut is "Q", if the buildings a adjoint, select all the adjoint buildings to square it) to keep a good shape and draw the building individually at your best.
https://www.youtube.com/watch?v=E1YJV6I_rhY

Happy Mapping!