Wood moves with changes in humidity. Temperature changes have very little effect on wood movement, unless the wood is very green, and it is very, very cold, in which case the ice crystals that form in the wood can render concerns about simple movement moot..
You want to acclimate your wood to the environment where it will reside when you're done working it. Therefore, if your benchwork is going into a spare bedroom, the best place to store the wood until you're ready to cut and shape it is,
wait for it...
wait for it...
wait for it...
wait for it...
the spare bedroom! :thumb: Ditto for the basement, attic, wherever. Remember, humidity is the main concern, not temperature. Cut, shape, assemble, etc as quickly as possible if you have to do so in another location, then return the wood to its destination.
Engineered wood products (not all of which are wood, but that's doesn't matter for our purposes) are more stable than natural wood. The primary engineered wood products for us to be concerned with are plywoods, particle board, medium density fiberboard (aka MDF) and hardboard, aka "Masonite". All are far more dimensionally stable than natural wood, but suffer from their own drawbacks.
The best product to make benchwork from is, in my opinion, shop grade plywoods, including the previously mentioned 1/2" birch. These plywoods are stable, simple to find, have few voids, and are fairly inexpensive. The biggest problem with them for the average modelrailroader making benchwork is the size, generally a 4'x8' sheet. Ripping the plywood down to size is a challenge, even for a well equipped woodworker. A very well equipped woodworker will have a panel saw or sliding tablesaw, and therefore will have no difficulty at all cutting it down. Fortunately, there are numerous ways for the rest of us to get our plywood rips, from having the lumberyard do it on THEIR panel saw, to plopping the plywood onto a pair of sawhorses, clamping an edge guide on, and going to town with the trusty Skilsaw. In short, it can be done, its just a bother.
Bothersome as it is, using plywood is worth the upfront hassle because it will greatly reduce the problems brought on by wood movement, problems that may take years to manifest. Unfortunately, when they do manifest, they are usually
major problems, because they affect the very foundation of the layout, meaning that solving them can be much more difficult than building the benchwork in the first place.