Brick is stronger and will last longer and depending on the wood might hold heat better (wood doesnt hold heat well, but masonary is very dense and as a result wichs heat well and you also have problems with moisture traping). I think that a wooden building (unless its a timber frame style) would be difficult enought to move that other than sentimental reasons it would be best to leave it behind, Since you will have lots of heavy things be sure you have your floorjoists very close together, if your sheating material is rated for 18-36 I'd go with joists 12 inches on center and use two layers of ply or OSD or whatever you intend on useing, also, concrete under the floor and maybe 1-2 inches ontop would be very good if you intend on keeping big tanks (it will make a floor so stiff you wouldnt believe it) and if that hasnt drained your budget enought get linolem flooring (not inyl wich is a plastic product but linolem wich is made out of linseed oil and oak dust) its waterproof and if you scratch it a little moving a big heavy tank and stand it self heals. Be sure to use 10 mill vapor barrior on the inside to keep the moisture from permeating your insulative material and freezing in winter (esentially turning your fiberglass batting into ice, wich doesnt insulate well) and if your budget still allows use greenboard for gypsym, especially if you can find fibreglass coated greenboard as apose to paper (green board is special gypsym formulated to hold up better with moisture and the new fibreglas skinned gypsym products leave no orgainic component for mildew to eat away at) That or you could build it right on the ground and make it leaky as a sive, its cheaper to build and if its only going to be run for 4-5 years or so you will save but if its much longer than that the heating coasts will catch up to you.
