I don't know whether it is different in Scotland (my answer related to England & Wales) but, as redcrx says, how would you sort out who claims what if each flat owner has their own buildings insurance?
If I was in your position I would want to know exactly what the position is and would look in detail at all the relevant documents of title and, if necessary, speak to the solicitor who did the conveyancing to get clarification.
Going back to your original question, I do not see how you can work out the cost of rebuilding your home unless it is done by estimating the cost of rebuilding the whole block & dividing it by the number of flats. Again, you need to get clarification of this. Your last point, about something you do causing the whole block to need rebuilding, ought to be covered by the insurance under a section concerning public liability for negligence which normally has a very high limit. (However, this also may be different in Scotland!)