The invention relates to a coarsening device, in particular to a roof surface coarsening device for building construction. According to the roof surface coarsening device for building construction, the time and labor are saved, the labor intensity is small, fallen cement mortar can be blocked, and thus hurt to people is prevented. The roof surface coarsening device for building construction comprises a cart and the like, a lifting device is arranged at the top of the cart, and a cross plate is connected to a lifting component of the lifting device, and supporting rods are connected to the leftside and the right side of the top of the cross plate; and a hopper is mounted between the top ends of the supporting rods, a material brushing device is arranged at the top of the cross plate, and amaterial brushing component of the material brushing device is located in the hopper. According to the coarsening device, through a water spraying device, water can be sprayed on the surface of a roof, thus cement mortar coarsens the surface of the roof better, and the effects that the time and labor are saved, the labor intensity is small, the fallen cement mortar can be blocked, and thus the hurt to people is prevented are achieved.