Apparatus and methods for constructing a shower pan. The shower pan is constructed from wedge panels having a foam core and facers on major surfaces of the wedge panels. The wedge panels are cut into portions that fit regions of the shower pan area. The wedge panel portions are placed in the regions such that the sloped upper surfaces of the wedge panel portions collectively form a continuous surface that at all locations slopes downward toward the drain of the shower. Pans for a wide variety of shower shapes and sizes can be constructed. The shower pan may be efficiently constructed on-site, often using common tools and techniques.