 His first job was collaboration with Arnulfo Villaseñor in the construction of José Guadalupe Zuno (at the intersection of Bosques and Union).By 1925 he was already a lead designer at the office of Juan José Barragán, a prominent builder of the time (he replaced Luis Barragán, who had left to open shop on his own).Around 1931, Pedro Castellanos founded Castellanos and Negrete, leading to a series of brilliant solutions to professional commissions.