Responsibility for balconies and terraces

[Citygate]

I own a flat in a large block built in 2006. The lease describes the demise of the flat to include the plaster on the external wall but not the wall, to the concrete slab of the floor and the ceiling so the flat has no individual responsibility for a roof. The flat has a terrace which is included in the demise and is for the sole use of the flat. However the lease makes no mention of a terrace (with a roof to a flat below) or balcony (no flat below). Nor does the lease make any mention of responsibility to provide a waterproof covering. (The terrace is also covered with a decking.) The agent says that the flat has sole responsibility for providing a roof within the terrace because the flat owns the floor to the concrete slab. The waterproof covering is, therefore, for the benefit of the flats below and the block in general.
Does anyone have any experience of this? If the lease does not mention a requirement (and in most other matters the lease is long and complicated) does common law say that the upstairs flat owner must prevent rain water coming into the flat below?

[jeffrey]

Rely only on your solicitor's advice (and certainly not on an Estate Agent's) about the precise text of the lease and how its plan applies.