What will be the tax implications if a person occupies more than one property for his residence? Can he treat all the properties as self occupied (SOP) and claim gross annual value (GAV) as Nil?
The SOP benefit (i.e., treating property as SOP and claiming GAV as Nil) is available only in respect of one property occupied by the owner for his residence.

If a person occupies more than one property for his residence, then the SOP benefit will be granted only in respect of any one property as selected by him and other property/properties will be treated as "Deemed to be let-out". Income from deemed to be let-out property is computed in the same manner as discussed in the case of "Let-out" Property.​

However w.e.f. Assessment Year 2020-21, a person can claim two properties as self-accupied house property.