Someone put out a call for dungeon modules to publish, and I'm considering... and that led to wanting to try to improve my Google Sketchup skills. I was able to do a few things in the past, but I was still having trouble getting used to the way Sketchup's interface works.
So, I went back and watched more tutorial videos on YouTube. It turns out that plan view + the offset tool makes dungeons ridiculously easy to make.
For those of you looking to try this, the secret is: top-down standard camera view and no perspective. Draw just the lines to symbolize walls, just as you would do on graph paper, but use Sketchup's precise measurement feature. When you have a level done, select all the outer edges and use the offset tool to draw a perimeterpne foot away from the inner wall (you can use a different measurement, depending on how thick you want the walls to be at a minimum.) You can use the push/pull tool later to raise the walls to the proper height. Select the entire figure you've drawn, create a group from it, and name it "Level 1". You can edit the group later to add features to the level. Hide the group and start again, this time working on Level 2. Once that level is turned into a group, unhide Level 1 and use the move tool to position one a precise distance below the other.
A word of warning, though: Google has sold Sketchup to another company, and there is some question about how it will be handled in the future. I would recommend not putting any models in the model warehouse or using models you haven't created yourself until there's more disclosure about what is happening, particularly in terms of licensing.