Hey again! Glad to see you're sticking with it! I just wanted to mention a nuance about building outlines that I wish I had realized when I was starting out. As tempting as it might be to adjust the alignment to better match the current imagery, it's actually much better to observe the general (mis)alignment of the surroundings, and maintain that in the shapes you add/modify... in other words, keep aligned to what's already mapped. This becomes more of an issue in densely packed situations where failing to do so can result in overlap.

One nice thing about the existing building shapes for L.A. county is that they were imported en masse, hence have good alignment to each other, as opposed to being drawn over time to different versions of satellite imagery. You'll notice that the imagery alignment can change not only over time, but in different areas at any given time. If you try some of the other (non-Bing) image sources available in the editor, you'll get an appreciation of how much the accuracy has improved lately. Cheers!