Pete,
I like to build kits. I was a AVID model builder as a youth. 1/24 scale cars, mostly AMT, and AIRFIX airplanes, mostly WWI and WWII. I think they were 1/87 or 1/72? I got pretty good with a spray can and my camouflage jobs (on the PLANES!) were real good. I used to win model contests at the LHS. I had many planes hanging, by very thin, clear fishing line, from my bedroom ceiling, in "dive-bomb" type poses.
I have several structures that I have put together. I also have purchased some "prefabs" too. It just kind of accelerates the development of the community if you can "plop" a few houses down, wire up the grain of wheat bulb and "light'em up"! Actually, even the prefabs get "the treatment". I weather them a little, I try to paint the insides black IF I can get a brush it there. It's MOST unrealistic when the whole building GLOWS!!
All-in-all I guess I have about a 60/40 mix (60% kits)at present and I have about five kits waiting to be put together.
I've never even SEEN a kit of N scale rolling stock.....course I've never "shopped" them either! I guess I'd have to say I prefer RTR rolling stock, since I've NEVER been "motivated" to seek a kit. Buildings are another matter. I WAY prefer to build, it's just the time...finding the TIME!
Marc