A pole barn is the cheapest thing to put up, and can be a simple "tent made out of wood" or something more elaborate. For stick construction, depending on the size you are building, you may be able to do clear span with no interior support posts and a center girder to support the storage floor.
It may help to look at the pictures of trusses in the <A target="_blank" HREF=http://www.trussnet.com/Resources/Basics/types.cfm/>Truss Resource Center</A>. You can get the storage you are looking for with attic trusses. These are commonly used in attached garages to add the "bonus room" over the garage and are sometimes called garage trusses because of this. They are engineered for the additional dead load of storage. The scissors truss gives you extra headroom to clear a lift. 24' is a real common clear span truss size, and 24' clear span fink and sometimes attic trusses will be in stock or a quick order item in larger home centers.
Condensation is a problem depending on where you live. I'm planning on storing implements and project cars inside the building(s) I'll be putting up, so rust is a concern for me and I'm stick building with wood.
Timd