I’ve used Quickbooks for Property MAnagement, and I think ERPNext can be configured similarly. Consider this:
Building = Customer Group
Flat = Customer
Tenant = Project
Issues can only be raised at the Customer level, so you may need a dummy Customer for each building to handle building-wide issues.
You can also copy the Doctypes into new Doctypes and give them meaningful names, remove superfluous fields, put some validation rules in place