Luke Brugnara is 32 and has decided what he wants to do with his life: He wants more of the same - to add to the 500,000 square feet in downtown San Francisco buildings he now owns. Watch More In a transaction completed Monday, Brugnara sold 735 Market St. and simultaneously bought 351 California St., better known as the Pacific Bank Building, and thus continued a very rapid and profitable streak.His portfolio may be worth $100 million - "75 million if you talk to a naysayer," said Brugnara. It began, for the native San Franciscan, at age 28 in 1993, when Brugnara bought a note for $1.5 million in bankruptcy court for the Kress Building at 939 Market St. He foreclosed on the former owner and leveraged the note with a $3 million loan, thus netting from it $1.5 million to close at escrow. "It was a no-brainer," he said. His portfolio now includes 814 Mission St., The Bulletin Building; 171 Second Ave., the Westinghouse Electric Building; 201 Sansome St., the Royal Globe Insurance Building; 939 Market St., the Kress Building; and 351 California St.