Guys thanks for all the suggestions. I've been trying some of the plugins, extrusion tools etc. It looks like there is no simple process but I'll take all your suggestions happily. Thanks again.

I've been trying to duplicate the irregular curved roof of this stadium in Lyon. Using an arc and then extruding line only gives me a symmetrical curve. As you can see the curves of the roofs seem to narrow so the edges can touch. Does anyone have a way this kind of roof can be done?