basis for depreciation will be the lesser of fair market value or adjusted basis on the date of conversion
Lesser of (FMV, adjusted basis). FMV is an estimated market price. adjusted basis is your original home purchase cost + subsequent home improvement cost.
Date of conversion: The date you put the house into service, e.g. ready to rent. If you made some home improvement after you moved out of the house, the home improvement period is BEFORE the date of conversion.
Usually I just use the county tax record for residential structure