I ordered my G25 online, so I had a couple days to measure my own car to get the exact dimensions and angles. I took very detailed measurements including angle of wheel, angle of seat, angle and distance of pedals to wheel, etc. My plan was to duplicate my car exactly. In the end, what I found was that I really did not stick very closely to the measurements I took.
My advice to anyone building a cockpit is don't worry about getting too specific on your measurements and replicating any particular car to exact specs. Most likely, in the end you are going to adjust quite a bit from your original measurements. For one thing, the wheel is smaller than a real one, so you cannot even have the correct dimensions no matter what you do. Also, in most cars the accelerator is farther back than the brake and clutch, so you cannot replicate that proportion either, unless you build a different housing for the pedals. If you are using something other than a car seat, the shifter won't be comfortable in the correct place. My chair has arms, so the shifter has to be forward a bit. etc.
I built mine mostly from materials I had around the house, and it wasn't very difficult to do. The top is 25" from the floor (probably could be .5" lower) the pedals are 5" from the floor; the Legacy GT dimensions would have the pedals higher, but with my chair, it would'nt sit quite the same. Also if the wheel was .5" lower, then the top rim of the wheel would be too low, so that means my G25 sits a little higher, and my sitting angle is a few degrees less than my car. There are a lot of things like that, but in summary, don't worry about getting too exact on your car measurements, concentrate on what will be comfortable to sit in for many hours at a time
my example is here:
https://www.gtplanet.net/forum/showthread.php?t=90066