PGBP :
If the main objective of business is rental income, and mentioned in AoA (incase of company), deed (firm) or the similar document, then PGBP (as decided by Supreme Court). In such cases, actual expeses, depreciation can be claimed as deduction.
IFHP:
It depends on the intention of the assessee, there is no wrong in treating the same as IFHP, if there is a constant treatment of rental income under same head. Standard deduction of 30%, Municipal taxes paid and interest on borrowed capital shall be allowed as deduction. Remains as non-depreciable asset.
Incase if treated as PGBP, the on sale of building, it looses the benefit of indexation. Thus there will be more income from Capital Gains as compared to Non-depreciable asset.
IFOS:
Incase where the building is let out along with furnitures, and the part of rental income from the furnitures is inseperable from the total rental income received from tenant, then income will be treated as IFOS. In such a cases, actual expenses towards earning the income, interest on borrowed capital and depreciation shall be allowed as deductions.
The above facts may be considered before considering it to be PGBP or IFHP or IFOS.