If there is nothing in your title deeds or your deeds are unworkable, follow the guidance in the Tenements Act.
The Tenements (Scotland) Act says that you should share repair and management costs equally, unless flats are of very different sizes.
So, if the largest flat in your building is more than 1.5 times the floor area of the smallest, then you need to divide costs by floor area.
To do this properly, you will need to measure the internal floor area of each flat. Do not include lofts or basements, unless they contain habitable rooms. Do not include balconies. The Tenements Act requires owners to give access to their flats to allow this measurement to be made.
When you have got measurements of each flat, add them all together and then divide the total by each flat’s floor area to get the percentage each owner should pay.
Legal reference
Calculating floor areas
Access for measuring floor area
