I’m not sure about your background with other CAD software, or for that matter familiarity with the general practices of creating architectural drawings. So, I’ll assume that we’re starting from the beginning here, and hopefully I won’t create trouble for having done so.
I think the first good habit to get into is to ‘Draw to Full Scale’ within SketchUp. Ideally, you should be able to measure a distance within your SketchUp drawing… and have that match the actual dimensions of whatever it is you happen to be modeling.
So to this point the first steps in getting started are to take measurements for the wall dimensions of the rooms you want to model. You can draw directly into SketchUp as you’re doing this. But the easier way to go is to just take some traditional pencil and paper notes as you’re going around to measure Wall Lengths, Heights, and the locations for each of the existing Doors and Windows. Nothing fancy is needed here… just a rough sketch with some dimensions on it so you don’t have to try and remember so much at any one time.
Start off with the Large General Aspects of the model, and work towards the details as you get closer to refining (and finishing the model). Rough in the Overall wall dimensions before you start adding in Doors, Windows, and and trim work you want to show,
By convention, as you’re measuring for your Door and Window sizes—Measure to the finished openings (where the face of the door jamb starts to cut through the wall), and not to the outside edge of where the casing or trim work stops… You’ll want to make note of how wide the trim work is too, and likely even capture the details of the profile if you really want to have a realistic model but these are the sorts of details that should be added in after you’ve made the basic cutouts in your walls to locate each of the doors and windows.
It’s not uncommon, in remodeling to tear out existing walls, and/or change door locations if room partitions get reconfigured. And by convention again, I think it’s worth drawing in ALL of the existing room elements, so you have them for a point of reference,… in order to show what’s being taken out, as well as whats being added in. Folks will approach the presentation of Existing vs. New Elements in a variety of ways… and you’ll be able to get some input on that here if you happen to need it.
As your drawing start to take shape. Look for and use opportunities to compare distances in your drawing to whats actually happening in the room. You can get some nice confirmation this way, and also catch some mistakes early own if you spend a little time measuring to a point from two different locations.
Unknown wall angles can be figured out by triangulating to a reference mark from two different know locations (e.g. points that have already been drawn into your SketchUp Model).
Very often you can use an offset reference line in order to measure back to something thats in too awkward a position to take plain linear measurements from. The radius of a curved wall for example can be determined by creating a chord and measuring to how far the rise of the arc is relative to the chord (/baseline) you’ve created… and Irregular walls can be measured at increments of every 6" or 12" from a straight reference line… and those offset points will be enough of a reference to help recreate the path that curve takes once you start inputing that inside of SketchUp.
Anyhow, these last few points won’t matter if your not dealing with unknown arcs, and irregular wall shapes.
The main message I’m trying to deliver here is that you should probably use SketchUp in an accurate enough way so you end up with a reliable, and scaled drawing when you’re all done. This is easy and rather trivial to do, if you start doing so right from the beginning.
There would be a lot of people who start by creating a 2D Floor Plan Drawing before they start in with the wall elevation views, and 3D modeling stuff.
You could give that approach a try to see if you like it. But there are also easy ways to create 2D floor plans directly from the 3D SketchUp model if need be.
Folks would use Floor Plan Drawings because it helps establish wall locations pretty quickly—and it’s generally a very nice way to keep a model organized, so you can double check that walls haven’t been pushed out of position during the rest of the modeling session, and stuff like that.