In preparation for “Home Delivery: Fabricating the Modern Dwelling,” a show on prefabricated housing that opens July 20, the Museum of Modern Art is letting the public in on the action. The museum has set up a Web site (momahomedelivery.org) that allows visitors to follow the process as five architectural teams create houses to be installed in outdoor space west of the museum’s main building. Every week until the show opens, each team will present progress reports, with photos, drawings and video clips of its efforts to make, ship and assemble the structures.