To create profiles in UrbanPaint users need to draw a series of connected lines / edges and arcs. They do NOT need to be welded, just all selected at the same time. Arcs can be problematic for UrbanPaint since it needs to model the profile along each edge of the arc. It is possible but results may vary. Be careful with arcs and creating intersections - that might cause UrbanPaint to not work. It is worth trying though!