I've been reading on the blogs of Iain, Chas and lnr about the woes of finding enough Evergreen half round plastic tubing for making gutters.
I didn't even know it existed, so have always made my gutters from pewter foil, cut in strips and pressed into a dip shaped in some styrene sheet with another bit of sheet with a bull-nose section on the end. I find long lengths difficult to deal with, so I make it in scale 10ft (ish) lengths as in the real stuff. It can be trimmed with a knife against the styrene "press". If you dig a little dip out of one end, you can press the last mm or so into that to get the widened section that the next slides into.
Pewter foil is obtainable from craft suppliers. It is generally know as Repousse Foil and is gold coloured one side, silver on tother. It has no spring whatsoever and is extremely malleable. It is easy to fold or press into other useful shapes, such as zinc flats over bay windows, church roofs, rainwater hoppers, etc. My Dad was at one time a craftsman plumber and I used to watch him making lead and zinc roofs, with special hammers, soldering them with a half pint bow lamp and a stick of Tinmans' solder. Working pewter foil is very similar in miniature.
I have no pictures of all this until I can find my old tools, so keep looking, I will make something up to show.
As with most fiddly sounding jobs, it actually doesn't take long.
BTW, I found that scale gutters look too wide, so I always make them a bit smaller. it is, ultimately, the look that's important.