Mostly scratch-built although because I don't have a shed/workshop I'm extremely limited in the size (and weight!) of machine tools I can have. My tiny lathe (Proxxon FD150/E) is absolutely fine for most of the lathe work but simply does not have the power to machine the wheels so I'll be buying them ready-machined rather as raw castings. He also machines them to fit the square-ended axles he supplies which will eliminate quartering issues. I'll be buying the boiler in too. Again my lathe isn't big enough plus I can buy a boiler cheaper than I can buy a decent quality propane torch big enough to silver solder the boiler up. Plus the commercial boiler will come with a boiler certificate so I won't need to go through the testing/certification process. I'll be buying the main frames for the loco and tender. I can get these laser-cut for not much more than I could buy the steel for. There's a few things like chimney, steam dome and tender axle boxes which I will be buying too but there's still an awful lot of cutting, turning, milling, drilling, bending and soldering to be done in order to arrive at a finished loco.