Just looking at what's available at level 492 (where I'm at right now), If you look at the recipes, they'll show an asterisk (*) next to any items you keep. Everything else you lose when you build something successfully. You don't lose anything (or at least, I haven't yet) when you don't have everything needed (like money, which I always seem to forget). One thing I'd point out; make sure the item you're building is actually better than the stuff available elsewhere. I made the mistake of collecting a bunch of Fenrirs (after I'd dumped them all, earlier) in order to make the Forged Helmet (36/35), but if I remember correctly, the Hugin & Munin adventure drop was better (36/36). Of course, I suppose if you have a ton of the ingredients sitting around (as I would have had, if I hadn't been so OCD about cleaning up the "clutter," it'd be worth it, and at least insofar as that specific blacksmith item went, there was no upkeep (but of course, at that level, upkeep should be completely meaningless anyway), but just based on that one bad example, I'm thinking I ought to think about it before I blindly go out of my way to build stuff.
