My 2D drawing program draws shapes as closed surfaces, but that’s all lost in DWG translation. All that comes through to SketchUp are the lines.
There are two basic strategies to using those lines:
- Group them if they aren’t already, and simply use them to trace over. As vectored linework, SU can snap to any end or midpoint among them. When you’re done, you can either delete the imported lines or hide them.
- Use the imported lines and try to build them up into surfaces and 3D shapes. If you’re at the editing context of the individual lines, tracing over some of them will make SU form surfaces from closed loops just as if you drew from scratch. If the lines are grouped, and you’re editing from outside that group, this action won’t happen. Once you have surfaces, you can start using the push/pull tool and moving into 3D.
There are details about whether your imported line come in grouped or not, or whether there are lots of lines crossing over each other that are issues to deal with, but without your specific file, that’s hard to advise.