Plan A has alot of up side but plan B does as well. How much money is on the note? Let's say 90 K on a 150 k home. So I have 90K at my disposal. I first would have to love the home and location and would have to look at neighborhood. Will your home retain value or are rental properties showing up there. Lot's of ifs, whats, what ifs come into play. I would probably go with B, refi the house at a much lower rate, pull the equity out, combine with 90k, build new home just the way I wanted financed at these low rates with that much down payment would be very low and short term. Rent the other home, with the refinanced rate, rent could double or triple loan payment. 2 morg interest deductions now, 1 earning income and will help pay the new one off. If money gets tight, you can pull equity from the rent home or frome the new home or sell the rent home, lots of options. I just got quoted 2.75% money to cheap not to use.