I don't know how to use Shetch-Up or any other similar program. I get many ideas, for projects, from every/any-where and I sometimes create my own modifications, when/where needed, as I suppose most hobbists do.
I have become proficient enough that I can often start basic construction (rough cutting, rough measures, ie., educated guesses) with many construction aspects, but when it comes to details for things like jointery fit dimensions, boards lengths, panel dimensions, I'll go to the planning table and draw out the exact measures and coordinate the correct cuts & assembly details. It is often at these times - detailed measurement figures, drawing/planning schematics, fitting via measures - that I may discover a previous measure/figure/ fit will need to be tweaked. If this detailed phase of the project was not fun, also, I would likely skimp on the exactness of the measures, figures, fits, etc., and my pleasure with getting a project finished, properly, would fall short. If I don't build it correctly, and enjoy what I'm doing, then the whole process would simply be a chore or task to be done. My hobby projects are not chores to be done!
*Repairing a tool is sometimes a chore, but at the same time, rewarding, because I know the end result will allow me to get back to doing the pleasureable work, using that tool. I like fixing (maintenance) a tool successfully, too, and sharpening a tool perfectly, etc. It's nice to have a good reliable (old friend) tool working well for me. Somehow (?), I enjoy the "company" of many of my tools and my shop. They are like old friends. They are not job- sites. Some old hand-me-down tools, somehow, I sense, come with the friendship of the previous owners, too.... and that's a comforting thought, too. (LOL, I think I'm getting into a foggy (Tao) realm, here, (like Grasshopper in Kung Fu, was it?), becoming one with the tool.)
There have been times when I build something, not that I need it for a function in my home or elsewhere, but I build it because I think I can. This initial thinking is part of the planning stage, I suppose. Later, I either find a personal use for it or give it away.
I know how to make many particular joints. I know how to make moldings/ profiles, I know how to make many of these kinds of specific "designs" or parts. The detailed planning for coordinating and assembling all of these parts is what I spend lots of out-of-shop time doing.... making sure all the measures/figures/dimensions/fits allow for the working/coordinating/assembling of everything properly.
It is rewarding to accomplish the building of a nice piece (excellent outcome). However, there has been times when I, personally, have been more gratified for having solved/created a particular design aspect/issue, within the piece (because of the detailed out-of-shop planning/measuring/figuring), than the satisfaction I've had with the whole of the finished piece. Somehow, I think, I have more gratification for solving/creating a detail, than if I were to rely on a computer program to solve/create it for me. .... Does that make sense? Not sure my meaning is clear, here. Maybe if I used (learned to use) Sketch-Up or something, I would appreciate what it has to offer, just like any other good reliable tool.
I think I got off on a few tangents, here. It's cold outside and I'm stuck indoors.... a scenario for ramblings on, that way. Sonny