I agree with what Spudfuzz and WednesdayAsh said.
Sketchup allows you to use the models for your comic, as long as you don't use it for commercial use (unless you purchased a license).
Aditionally, I've made 3D models before (although I don't post them online, since it's simply not my focus), so I'd be flattered if they were used in someone's comic to be honest.
And pros use Sketchup all the time. Yuumei, Tsulala, Feigap, and many more!
If you learn how to use the program, it's a skill and not a crutch.
A lot of anime artists also use 3D programs to draw backgrounds, so use any programs available to your advantage. I'm not a big fan of those who don't trace the backgrounds (they just take the model and put it in their comic) because things just feel out of place. Of course, that's just my preference and some comics can make it work better than others, such as Killing Stalking.
However, I would also recommend learning perspective, since it will also be helpful to you when you want to add extra details to your buildings and such.
Or maybe you want to slightly exaggerate some buildings proportions just to match the atmosphere or a certain scene and such. So learning both would be good. \o/