Allocation of expenses

I am secretary of a large complex consisting of 163 apartments, 16 retail shops, a Coles supermarket, & council car park. We are having tenders to replace the roof membrane which will be expensive, well over one million dollars & we have a dispute in the allocation of the cost between the four stratums. Our Strata management statement lists Building Facade allocation as 97% Residential, 1% Retail, 1% Supermarket & 1 % Council car park but no mention of roof.

The residential Owners Corp feel that this allocation is not fair as all entities should share the the cost more equitably.

We have suggested that the allocation would be more equitable if the costs are allocated on the ratio of relative floor area that each entity occupies i.e. Residential 68%, Retail 5%, Supermarket 5% & Council carpark 12%.

My question is are there any similar complexes that have cost allocations specifically related to roof or where can I go to get this information.

I would like to have this information before reverting to mediation as the three entities will not agree to the change suggested.