You're playing Luncheon of the Dead
Luncheon Of The Dead is a survival style Real Time Strategy game, wherein you control 9 defenders trapped inside a mall. Your job is to survive as long as is possible. You must scrounge for supplies (ammo, medikits and debris) in the stores of the mall, build walls of debris to hold back the shambling hordes and position your defenders to shoot the zombies without getting eaten. Upgrades can be purchased along the way to give your defenders a leg up, and if things get too hairy, you can always drop a Molotov Cocktail and BBQ some zombies!