It really depends on the type of wood. Cedar or redwood will weather the best. That is, it will retain it's natural reddish color longer than others, including teak. Regardless, they will all eventually weather to various shades of gray if left unattended. I've had a cedar garden bench that is over 15 years old and still looks good with the original color still prevalent. I sand it lightly in the winter months and then brush on spar varnish. There are other products that will probably do as well. Keep in mind the most damaging thing outside is ultra-violet sun rays, rather than rain. BTW, if you do go with cedar or redwood, be sure to let it age for a few months before finishing. The natural oils that protect the wood leach out somewhat and it will retain the finish better. I'd say steer clear of teak, unless your up to constant stripping and refinishing... At any rate, best of luck!