well, it's nice to be able to move around your scene, find an angle, push some blocks around to that the composition fits your new angle and voila! you've got your basics drawn out and ready to be designed on top of. Of course, you still have to find your vanishing points and horizon line, but you've been able to explore the possibilities with out much cost.
You really shouldn't be approaching it that way, you'll just be giving yourself a crutch and never tackle the actual problem (which is you not knowing proper perspective). You're going to have to place characters in those scenes, you'll want to change things and add things which will all require you to know perspective.
More so then that, perspective is probably the easiest thing to learn. Draw your horizon, set your vanishing points and voila! Here's a nice tutorial; [link]
Wonderful work! I'm very impressed by your creative use of Sketchup. Very inspirational. If you ever find that you would like to talk about your process, either in a tutorial or some other format, I am definitely listening.