An awning supported on roof panel for use outdoors mainly includes an automatic shade roller, a plurality of supporting frames, and a plurality of adjustable sucker units coupled with the supporting frames. Each of the supporting frames is provided at two lateral sides with two elongated slots, in which the sucker units may be shifted to a desired position relative to the supporting frame. The supporting frame is integrally provided below each lateral side with two vertical framing walls, and at a central top portion with a raised pad that has two mortises formed at two diagonally opposite corners. With the above arrangements, the shade roller, the supporting frames, and the sucker units may be easily assembled for mounting on a roof panel to provide an awning for use outdoors without using any tool.