I guess I'll jump in head first, like I do in everything else.
I've never used any CAD programs before, but I hope that having used a few vector drawing programs along the way might help. We're building a house on a wooded lot and working with an architect on the design. He's great to work with and always open to suggestions.
So far, when I've had ideas for plan changes, I've taken the PDFs he's sent and imported them into GIMP where I could redraw it, but that's getting quite frustrating. I tried downloading Autocad, since I figured most of the work would be done in 30 days, before the free trial is up, but every tutorial uses the Windows version, so the Mac one is confusing.
Since I use FOSS in almost everything else, whenever I can, I found LibreCAD.
While I'm learning this with the goal of using it in this one project (the house plans), I'm hoping that I'll find it comfortable enough to use that I'll find it easy to continue to use in planning out smaller projects in the future.