I thought i tried to attempt that but failed.

In designing homes, buildings or ships, it would be awesome to select lines that will make profiles or surface or even solids that all extrude together in one step.

A nice future touch might be allowing the user to define how to do cuts or end treatments so that wood or steel crossing another member would be automatically trimmed and (in the case of steel beams) treated with weld of a given or of an industry accepted (or FEA-recommended) weld. Alternatively, an experienced designr could just apply an arc and extrude it as weld along the path. But, if that, too, were doable automatically, it would take out rules of thumb for estimating weld weight and provide an actual, or more accurate, weight estimate. But, it might also add a lot to the file size. Alternatively, to that, the weight could be mathematically derived and a "placeholder" drawn only when the view is zoomed or printed...