Here is the finished product. Note that it does not look as clean as the linked drawings, as I am not a great woodworker and I made a few mistakes.
Quite a few years ago I got a Logitech G25 for Christmas. It was a vast improvement over keyboards, joysticks, and mice that I had been sim driving with for years. Unfortunately, I did not have a good place to set it up. After years of using janky wheel-clamped-to-desk-with-pedals-on-the-floor setups, I finally moved into a place where I had enough room to make a dedicated sim racing space. After another few months of being too lazy to do it, I started taking measurements from my 1991 Mazda MX-5 Miata, which fits me like a glove, to build a proper sim cockpit.

After searching the web for a week or so for other examples of similar projects or commercially available products, I found a simple enough design I liked and began to design my imitation version from the measurements I took from my car. Another few days later, I had designed all the pieces and managed to lay them out in such a way as to fit within a 5x5 square - the size in which Baltic Birch plywood can often be found. A few phone calls after that and I had located a lumber yard not far from my house with the requisite wood and the next day I had it in the back of my roommate's truck and on the way home. Finally, after a week of cutting out pieces, drilling holes, and screwing them together, it was finished.

Naturally, there were a few mistakes. First, the shifter didn't even fit. I had to move the panel it was supposed to attach to about two centimetres back, and the rest of the assembly two centimetres forward to compensate. Then after trying it the first time, I realized the wheel was about 3.5 inches too high (why I'm so inconsistent with units I don't know. I blame the US for not adopting the metric system when they had the chance. That's 90mm for the rest of the world). After fixing that, I finally screwed down the seat rails I had left sliding on the base for months; I tried to estimate where to put them to center the seat and ended up around two inches off. Finally, earlier tonight, I undid that and moved them to an appropriate location. Now it rocks!

If you want to build your own sim racing console, you may or may not be able to use the plans here. I think it is quite likely you would be able to use them with at most slight modifications, and I will try to call out where that may be necessary in the following paragraphs, but do make sure you have enough space for whatever you build and that you will fit in it comfortably! If you are not sure how to determine those answers, make educated guesses; that's what I did for most of this process.

As designed, this should fit a Logitech G25 (though it shouldn't be hard to fit any modern wheel/pedals/shifter combination with some modification to how it mounts) with pedals either on the "floor" or (taken out of their plastic housing) upside-down against the front wall. The bolt holes are meant to approximate the positions of the pedals at rest in a Miata; if I were to do it again I would probably move them forward somewhat, as the G25 pedals have much less travel than the Miata pedals and feel a little unnatural as close to the driver as they are. Keep in mind, the Miata is a small car, and you may want to build yours slightly larger. I am around 5'9" (1.75m) tall and find it fits me well. As always, your mileage may vary.

My chief complaint with the unit as it is is being hard to get in and out. If you have lots of space and can put it in the middle of a room, or with the shifter against the wall (or if you omit the shifter or mount it on the same panel as the wheel) you will not have this problem, or it will be greatly reduced. As mine is, I have to step onto the seat, then gradually lower myself as I walk my feet toward the pedals. Taking the steering wheel off makes this much easier, but also requires putting it back on. As I am still young and flexible, this isn't much of a problem, and well worth putting up with for how much better it is than clamping the wheel to a desk. The only other problem I occasionally notice is my knee bumping the clamp for the wheel; this only really happens when I left-foot brake, and I've learned to avoid it. Those with longer legs will likely want to mount the steering wheel slightly higher.

Below are some photos that should be helpful should you choose to pursue such a project and descriptions that should help you interpret their importance. In addition, I have both sets of drawings - those I initially made to construct my console and a revised set fixing the problems I encountered during construction.

I believe at one time I had intended to mount a display on the panel above the steering wheel; I ultimately opted instead to mount it to my desk such that it could be swung in front of the wheel or over the desk as appropriate. This is nice because at the moment I only have one display.
Here you can see the pedals mounted against the front wall, with the holes below them to mount the same pedals in the plastic housing they originally came in to the floor."
The seat mounts are pretty simple. I made a bunch of relief cuts in the end of a 2x4 with a saw to approximately match the angle of the ends of the Miata's seat rails, then smoothed them down with a file and drilled the holes for the large pins behind the bolts. Tapping wood this soft is hard, and only one actually worked well enough to thread the bolt into it; using a different kind of fastener or epoxying a nut in the end of the mount would probably be better. There are two holes in this because the Miata's driver and passenger seat rails have different widths; I wanted to be able to use either.
I initially attempted to mount the seats using measurements and intiution (mount them the same distance from the pedals as the real car, and split the difference between the driver and passenger seat rail widths to determine where they go) this was a bad idea. Sitting in the seat it was immediately obvious that it was too far to the right. I remedied this by undoing the screws, mounting the seat, and sliding it around while sitting in it to determine the ideal location. I then marked where the 2x4s were, removed the seat, and redrilled the holes and screwed them in place.
Here you can see how the wheel mounts. Depending on how much wood you have you may be able to make the piece the wheel mounts to longer for added rigidity, though this will likely be unnecessary. The Sim-fixed drawings reshape the sides so that the panel doesn't stick out as it does in mine. For extra leg room, cutting the corners out of this panel may be helpful as well.
I did not mark most of the fasteners in the drawings; I did mark the locations of the holes needed to secure the wheel, pedals, and shifter, as well as those to secure the sides to the base, but left out the others. This being a high-stress area, I wanted something better than the wood screws I used elsewhere; I believe these are all 10mm bolts, and there are five on each side of the base as well as two on the shifter, which can be mounted on the right or left for right- or left-hand drive cars. For everything else I used 2.5 inch wood screws from Home Depot; I think I used about a box and a half in total. Most parts are fastened with three screws, one close to either end and a third in the middle.