A composite picc will be fine outside. It's basically plastic, so weather isn't going to affect it like wood. See if you can find a model with both head joints, and get the best of both worlds metal/woodish. Check craigslist to see if there's any deals. Also look into WWBW's composite picc--I've never played one, but I have heard good things about it. Not the greatest horn, but a nice decent player.
Although honestly, there is absolutely no reason you can't play a metal picc inside. I played the piece of crap Artley for years. I still play my silver Gemi for band, even for our few indoor concerts. It depends on the song, if I play the wood or the silver. For example, the folk songs I used wood; the Journey medley is on silver. Our director (who is very outspoken) has never once commented about me on metal. And our resident professional composer insists I play my silver--he prefers its sound over the wood's.
Really, it's all about control, rather than what the instrument's made of.
Flutes:1975 Gemeinhardt M2 in chrome nickel;1982 Armstrong 80;2006 Yamaha 584
Piccs:1978 Artley piece of crap 15 P;1982 Gemeinhardt 4S;1980s? Armstrong all wood (no model)
Bass:2006 Jupiter di Medici G0199
Treble:20?? Guo New Voice
+ many flute-cousins