I have made this type of wheel for the big Nikko, the D shape.
The edge is serrated as the guy using it prefers to to rotate it with his thumb while holding the rifle still, and the range tape surface is 12mm flat. Overall diameter is 140mm, lots of choices in design and shape.
Made of Laser cut Acrylic in three pieces, and all up with machining and fastenings it cost $80 NZ to make (= £35)
This one is a recent design, with a Yang shape. The minor diameter (around the scope knob) is 80mm, slowly enlarging to the major at the tip of 220mm. OK it does have a very large diamter, but is rotated out of the way for storage. Again in Acrylic in 2 pieces, clamps to the scope knob with 3 grub screws. It cost me about $NZ45 to make, (= £20)
I'm gradually designing new shapes, all depending on the scope and rifle, and paying close attention to how the shooter uses and reads the wheel.