I'm working on the house body now, and even though I wrote this in another thread already, it really belongs in this thread.
To try to get the right dimensions on all the small scale features, I typically try to find a couple of measurements from a spec sheet, and then scale a photo or diagram as a canvas in Fusion 360 to match the known sizes.
E.g. from the spec sheet of the CAT 390F excavator, I can see that the length from the center to the very back (the tail swing radius) is 4.70 meters, and the height from the ground up to the counterweight is 1.64 meters. I insert the canvas and then scale it to match the known measurements (just divide by 14, since the scale is 1/14).
After the canvas has been scaled properly, I can draw in the 3D-objects on top of it to match the sizes of the features.
Insert canvas:
Switch to orthograpic view:
Draw in the objects:
Switch back to perspective view:
Hide canvas:
Voilà!
Best regards,
Stein :-)