A modular roof system for a building and method for installing the modular roof system includes roofing modules (M) which are designed to be arranged alongside each other substantially with continuity on a supporting structure (C, T). Each roofing module (M) includes a supporting base (20; 120) which is designed to receive at least one functional element of the roofing and rests on the support structure (C, T) in an installation condition, and a top covering part (22; 122) supported on the base (20; 120). The base (20; 120) is shaped so as to define at least one free channel (26′; 126′) extending substantially along a first direction of juxtaposition of the modules (M) and each roofing module (M) has interlocking members for joining together with adjacent modules (M) along at least one direction of juxtaposition of the modules (M).