It almost goes without saying but flight simulators tend to be fairly large devices. Now there are certainly some "desk and chair" models, however those simulators tend to have minimal (or no) regulatory standing, which may limit their usefulness. The size of a simulator is a byproduct of needing to have a realistic cockpit and the nature of the visual system. Before you sign on the dotted line and buy a flight simulator you'll need to evaluate just how much space you can economically devote to it.
Compact Flight Simulators
The smallest simulators with regulatory approvals tend to be the most basic. They generally do not have an enclosed cockpit1 and instead are generally a chair with a control panel attached to it, and a visual system which consists only one to three forward LCD screens. Sometimes only one LCD is used to further reduce cost and space. Simulators like this typically require only an area about the size of a sub-compact car. They're usually very economical and can be quite useful for many kinds of procedural training, for example, maintaining IFR proficiency. These also tend to be the least realistic simulators.
Medium Size Flight Simulators
This is where you're going to find most of the simulators with useful regulatory approvals. They tend to have reasonably or absolute realistic cockpits and larger visual systems. The visual may still be LCD based but there are usually at least three LCDs providing around 90 degrees of forward visual coverage. Some will have five or six LCDs providing a better visual with more coverage at greater expense. At the higher end these systems they will have projection systems which provide a wide field of view often 160° or even more. The vertical field of view ranges up from from 40°, with helicopter flight simulators tending to have much higher vertical fields of view. This is of course more immersive, and more expensive. A wider field of view however means the pilot can look around to locate the position of things in the world without turning the aircraft. In a simulator with only a small forward visual area the pilot is effectively wearing blinders and is unable to turn their head. For helicopter simulators the vertical view is actually as important, and maybe even more important than the horizontal. The larger vertical view makes it possible to practice hovering which is a most important skill set for the helicopter pilot. This is a major reason why until recently simulators were not used for VFR training. Today, it is not unusual to use these devices to enhance hover training. As little as 15 years ago hover training was generally introduced at about the 10th to 12th hour of ab-initio helicopter training. Today the training starts very early in training. These simulators will typically require quite a bit of room, 400 to 1,000 square feet (47–93m²)
Large Flight Simulators
The largest2 flight simulators are generally Level C and D Full Flight Simulators. These are highly advanced type specific full motion simulators. Generally they require a large multi-story spaces. Beyond the simulator itself there is usually a control center, power facilities, and other support equipment. It's not unusual for operators of this kind of simulator to build buildings specifically for them.
Flight Simulators in Trailers and Containers
A popular choice for smaller flight simulators is to house them in a dedicated trailer or intermodal container. This allows an operator based out of multiple locations to move their simulation facilities between those locations more easily. The trailer can be towed, or dropped off at a commercial carrier who moves it for the owner. The later being a very cost effective option for long distances. If the simulator is to be moved by ship it must be built to handle that or salt water and moist air will destroy the simulator. NexGen Simulation's parent company has an OEM trailer manufacturing division which can fabricate custom simulator trailers. It should be noted that when a simulator is installed in a trailer that generally restricts the level of regulatory approval. All of the FTDs (both EASA and FAA) when they become more complex require re-certification when they are moved. This results in trailer installed systems approved as FNPTs or AATDs, which do not have that requirement.