A picture of a building with a round or circular roof. Note that this building has its circular roof worked out only half (full round roofs exist aswell). This kind of geometric structure is already better than fully sloped roofs (stronger if comparative materials are used), yet is still worse than a truly "flat" roof (the latter being more efficient and allow easier access). Also note the gutter/rain pipe, which is circularly shaped as well
<a href="//commons.wikimedia.org/wiki/User:KVDP" class="mw-redirect" title="User:KVDP">KVDP</a>
<span class="int-own-work" lang="en">Own work</span>