This chair is in 1:6 scale, but you can do it in any scale, you just need to find a plastic bottle that is of suitable size. The instructions are not complete, but you should be able to make this chair using them and a little common sense.
I used a 1.5 liter mineral water bottle for the chair. For the upholstery fabric, I used very stretchy fabric, because it was easier to get that to form neat curves. I used PVA glue and although that does not stick that well to plastic, it is not a problem as the various parts of the chair are glued to each other in so many places that when everything is in place, they won't come loose.
First you need to decide the shape of the backrest. Make a paper pattern of the backrest and trace that to the bottle using a permanent marker. After you have done that, cut the bottle with tin shears.
Make a hole well outside the cutting line with a Stanley knife, so you have a starting point for cutting. It is easier to cut the bottle, if you first cut a little outside the line, removing most of the excess, and then cut along the line to get the final shape.
Cut also a suitable length from the bottle neck for the leg of the chair.
This is the leg assembled and covered with fabric. The bottom part is a lid of a round cardboard box (I think that was a gift box). You can use any kind of lid or even make that part yourself. The most important thing is that you need to be able to make a round hole in it.
This is the leg shown from below. The round hole is exactly the size of the bottle neck and the threads keep the bottle neck in place. So, you need to make a tight fitting hole and screw the bottle neck in it. You can use glue, if the chair does not need to revolve.
For upholstery, you need felt for the backrest and felt or some other filling for the seat. I used two layers of felt for the backrest. The first layer is exactly the size of the backrest and the second layer is bigger, so it could be folded over the edges and glued behind the backrest. The seat has the same fabric that was used to cover the leg. Underneath the fabric, the filling is placed so that the result is even and soft. The placement of the filling depends entirely on the shape of the bottom of the bottle.
This is the same seen from behind. When gluing the felt, you need to make sure the flaps do not overlap or the result will be bumpy.
Next, you need to cover the seat. Glue the front edge of the upholstery fabric under the chair and tuck the back edge between the seat and backrest (put a little glue in there first to make sure the fabric will stay in place).
Glue the upholstery fabric to the backrest the same way as you did with the felt. Tuck the bottom edge between the seat and backrest. Be careful when putting glue in there, because you need to make sure there will be no glue in the parts of fabric that will remain visible.
The chair should look something like this at this point.
Now you need to cut the back side of the backrest from thin cardboard. Use the backrest pattern, but make the shape a little wider. Check that the width is correct and then cover the cardboard with the upholstery fabric turning the edges of the fabric over the edges of the cardboard and gluing them there the same way you did with the front of the backrest. Glue the back piece in place behind the backrest. The back piece should cover all the upholstery fabric flaps on the back side of the backrest. Finally, glue the leg in place.
Here is a picture of Tiny Kitty sitting in the finished chair with a small pillow made of the upholstery fabric.