My neighbor and I just built a 14' x 20' frame building wth metal rib siding & roof, and a gravel floor. It holds two kayak trailers and all our gear. Total cost $1,100.00 U.S.
We bought the siding cut to length from the local lumberyard. Bulding time was about 60 hours each over 4 or 5 weekends. (We built it this spring when the paddling weather was crap)
The biggest advantadges to the metal builing are security and durability. With more than $8,000.00 invested in boats, trailers, and gear, We wanted something that wouldn't blow away or Walk away. The Wood frame makes it easy to hang up all the gear and even the extra boats when they're not in use. We insulated the roof so it stays fairly cool in the summer if you wanted it to double as a workshop. (It might heat better in the winter as well)
More expensive than plastic & pvc pipe but we've been really happy with the result.