(MONEY Magazine) – Tired of low ceilings in their upstairs bedroom, no shower in the nearby half bath and a flight of stairs separating them from their young son at night, John and Susan Herbert decided to raise the roof of their 1942 Cape Cod. The initial plan for their 1,593-square-foot, three-bedroom house in St. Louis Park, Minn. was simply to build two dormers, which would have given them more overhead space in the bedroom, and to squeeze in a shower and a small upstairs bedroom. Total cost: $125,000. Then they discovered that for another $75,000 they could build an entire second floor, complete with a master suite, two new bedrooms and a full bath. The work took six months, though the Herberts had to move out for only a week. The resulting addition, which tacked on 573 square feet, looks like it's always been there. And the extra upstairs bedroom came in handy when the couple had a second son last year.