Yes, the roofs come off each of the buildings in the compound. Andrew then very cleverly designed the main building in several sections above the ground floor level, so various parts could be exchanged for damaged sections (the rationale being that the surrounding walls and buildings would shield the ground floor from incoming artillery fire). So, as well as the 3 flat roof sections being removable, the whole top floor level of the centre section comes off, as do the covered balconies on either side of the portico, and also the 'bay window' on the right hand side, all allowing easy access to the interior.
Still got to make 2 versions (undamaged and damaged) of the memsahib's garden at the back of the Main building and I think I need some piled up barricades to properly block the 2 gateways at the front and rear. Also considering a striped awning for the portico balcony for a bit of added colour, as these appear on several pre-siege images of the Lucknow Residency.