Common Expense Allocation

[Paul True]

I have searched far and wide turned up little on the matter of common expense allocation. So what is the proper way to allocate common indirect expenses not attributable to any one property across a range of properties including land and not in service locations?  Should they be allocated uniformly to all properties including land or not in service locations. Should they be allocated as percentage based on income of the properties, or allocated uniformly only to active in-service properties? Should they be listed as a location on the return rather than being allocated to individual properties? I have on CPA that did one way, another that did something else and one that seems to make more sense to me. Fully confused. Help will be appreciated.