You've got an incredible set of flight controls. Your panel has no equal and your scenery would fool a naturalist. What's next?
Clearly you need a flight deck enclosure to match. Perhaps the ultimate is to use the real thing. Buy the front end of a retired airliner and install the wonders of your sim within. Don't laugh. This is actually a viable approach. Earlier models of commercial aircraft, notably 737 and 747's, having had an exemplary career moving people about the globe, and having reached the allowable fatigue life mandated by the various federal agencies, are now being scrapped. It's possible to buy a portion of these scrapped beauties.
If you pursue this route expect to get a piece of equipment that looks like the owners got the full value of their investments out of them. It is, after all, being sold for scrap. Still, it will be authentic and if you complete your sim with it you will have some richly deserved, serious bragging rights.
Of course, there is nothing that says you must limit yourself to airline salvage. Pretty much all aircraft models eventually end up in a bone yard somewhere. All salvage is potential material for your efforts. You might just find that a smaller aircraft makes more sense. It will likely be less expensive as well as being easier to park somewhere in your home.
If this is your road less traveled, you might start by browsing through Trade-A-Plane. Look for outfits that deal in older airliners and make some phone calls. This is also another of those situations where a few polite emails to fellow flight sim enthusiasts may be of value. Ask where and how they came by their prize. If you can't quite bring yourself to part with the necessary cash for a scrapped, heavy flight deck ($10K?, $15K?) consider J. K. Dunkley's approach. Buy a junked car. It probably will be much less expensive and provide you will a strong starting point.
Actually, this is not a bad segue into a short side bar to mention strength considerations for the enclosure. Your flight sim cabin is not just a bit of visual magic to support the illusion; it quite possibly needs to be considered as a structural element as well.
If you anticipate developing a motion system, keep in mind that the enclosure must simultaneously be strong enough to tolerate continual rocking and rolling, and be light enough to be rocked and rolled. The strength required is a non-trivial issue, especially if you're planning a sim based on an airliner (they're not called "heavies" for nothing). Your enclosure may well be supporting a collimated display as well as overhead panels in addition to your own weight and that of your co-pilot.
A big sim incorporating a motion system will require a lot of planning to get it right and make it safe.
****end of side bar****
If you've got the money the people at East Point Military Museum will make a fiberglass B737 shell for you.
If a fiberglass shell doesn't send you and if you have decided that aircraft salvage or junked cars just aren't going to work either, you might give some thought to building it yourself. There are a great number of materials at homebuilder's supply stores that one might use. Be open minded and creative. (While I personally would not use stucco for my sim, I can appreciate that it would be relatively inexpensive, fireproof and not bothered by termites. If the material works for you, go for it!)
While the specifics of your enclosure will depend on your particular circumstances and desires, here are some things you might consider.
Plan. Use paper, cardboard models, or a CAD system, just try to make your mistakes in the planning phase. If you need basic CAD software, you can get a free 2D CAD download from Turbo CAD.
Think modular. Sooner or later you're going to want to move your sim. It's amazing how the weight builds up. It's amazing how narrow doorways turn out to be. An enclosure that is designed to be broken down is both easier to move, as well as easier to build in the first place.
Watch the weight. Smaller projects can easily be fabricated from chunks of ply, but as the projects grow the weight goes sky high (couldn't help myself). There seems to be a natural movement toward 2 by 4 lumber and heavy plywood or worse, even heavier particleboard. It's better to use clever design to gain structural strength rather than large chunks of wood. There are no timber-framed airplanes. (Technically, this includes the Spruce Goose because they didn't limit themselves to wooden pegs for fasteners.) You're not building a house; so don't frame your sim like one. (That is, of course, unless you actually are using stucco.) Using ¼" ply with furring strips to form skinny wooden I-beams will give equal or better strength for less weight, plus it allows you to more easily form curves. This is close to the way aircraft were made years ago. It still works!
Think robust fasteners. If you plan on frequent removal of portions of your sim, panels for example, consider using some sort threaded metal connectors. For instance, you can more or less permanently fasten angle aluminum to the structure of the enclosure. Tapped holes in the angle can be used to hold the panels in place while allowing easy removal. An alternative is to use T-nuts to back up holes through the enclosure's structure as attachment points for panels, or even to fasten various pieces of the hopefully modular enclosure together.
Use plastic foam. Dry floral foam is open cell urethane foam that is used for silk flower arrangements. It is cheap and readily available from craft stores. You can easily form complex shapes by carving and sanding this foam. Use it to make to make such things as the blended trim that surrounds recessed windows. Once formed, the foam can be covered to protect it from being dinged or crushed. Fiberglass works extremely well for this, but it's not high on my list of suitable materials. Fiberglass is most often used with epoxy resins that eventually lead to allergic reactions in many people. There are vinyl ester based resins that are less likely to produce allergic complications, but both resins (and the required glass fiber cloth) are relatively expensive and just down right messy. Instead, use paper and water based urethane varnish. Start off by covering the foam with a light coat of varnish to seal it. The foam is extremely thirsty and will suck up an amazing amount of liquid if you're not careful. You don't want this to happen, as it will take forever to dry, so give it a light coat and let it dry overnight. Putting the paper on is simple, with one caveat. The water in the varnish will cause the paper fibers to swell. If you stick dry paper on wet foam, the paper will develop wrinkles. The way around this is to wet the paper with varnish first, let it set for 20 or 30 seconds, then put on the foam. Smooth it with your paintbrush and move on to the next piece. You can put about three layers on at a time and not have an impossibly long drying time. Somewhere around 10 layers total will give you a pretty firm surface, so you should plan on spreading this out over several days. If you have developed lumps or bumps from too many overlapping paper pieces, you can carefully wet sand it to smooth it out.
Use automotive upholstery techniques. Consider making wall, trim and ceiling panels (we're not talking control or electrical panels here, just the upholstery kind of stuff) for your cabin interior in a fashion similar to methods used in automotive refurbishing. Basically, the panels are simply 1/8" masonite covered with a vinyl fabric. These panels are somewhat flexible, are easy to make in odd shapes, and look great. Glue the fabric on with spray contact cement. The panels are held in place with broad head screws. Of course, if you're patterning your sim after a military aircraft, you'll probably just want to paint the Masonite.