To cover a trans hub there are several ways to do it. First an for most is to start with patterns. I use heavy card stock called tag paper. It is the material to make the yellowish paper tags. Most hobbyist donut have the stuff so I recommend getting heavy shipping paper (brown stuff to wrap boxes) and start taping it together the size you need.
Start by making the large flats that go under the seat butted right up to the trans well. Make sure you do both sides and mark them as R and L and the face up side. You will be surprised how different one side to the other is even on the straightest car. Some wells are even shifted off center by design.
Next make the patterns for the "hump" start at the firewall and trim the edge so that it has a lazy arc meeting the firewall (if you are lucky, 90% of the time you wont be) this curved shape will carry all the way to the back. Since it probably wont, make the cone smaller at the back to where the tunnel narrows, leave excess for later step. Crease the papers edges where it meets the floor but don't cut off the excess.
Then go to the back of the car match an arc to the roll pan at the rear of the car and work to the front in the same way (again leaving the floor crease long. You want to start with an overlap over the front piece. Cut the shape you like on the front of the rear tunnel paper (if your are going to bind) If not make it straight across with an extra 9/16" over lap of your finished line.
Now you have a decision to make. Will you sew the pieces together, bind them individually or Bind them together. If you sew them you need to add the material needed to sew them together called salvage. On carpet I always use 9/16" mark the Hump patterns on the creases with a circle compass set at 9/16" and pull with the pointy end of the compass on the crease. Cut it off excess when done. Next trace the overlap line from the rear part of the tunnel cover onto the front cover. The set your compass to 1 1/8" put the pointer end on the line of the front and add the material to the back, cut off the excess.
For newbies at this I generally recommend only sewing the tunnel together and binding the floors but lets say you want to give it a go.
Next. trace the tunnel salvages onto the floor parts, you will have to add extra paper to the inboard edges of the floor piece if you have done it right than a 9/16" strip will do it, but add extra and make your life simple. then using the compass and the drawn line mark the 1 1/8" with the compass off the marked line and cut off the excess.
Now here is the trick. Never do a fit up with carpet it is too expensive. Use a piece of cheap material. I have all kinds of misc. junk fabric. But you probably wont. I would get a couple cheap twin bed sheets. Cut out your shapes from it and sew it together. Lay it in and see if it fits. Adjust the patterns where necessary for fit.
Now Carpet is harder to sew and this thicker. When you sew it together don't take a 9/16" seam it will never fit, the carpet thickness make it shrink up, sew it at 1/2" for 1/8' pile and 3/8" for higher pile. In the end the salvages will need to be snipped to make them more pliable. Bind the front and if the side and back are exposed bind them too.
I like leather binding the best but I have used 1" nylon webbing too and it looks pretty tough. We have a few carpet stores here that will yarn bind but that stuff is unforgiving when pinched in a door.