If you really want to do a custom Hub you can get a quote from emachineshop.com
http://www.emachineshop.com/
They have software that you download and then you make the part. It will take a little time to get used to their software and does require some machining knowledge (but not much). The best part is that you pick the processes, material, and quantity, then press quote and TaH DaH! You have a price and you can order it. Typically it takes 3-4 weeks to get custom parts (that is why it isn't the greatest FIRST Resource).
If you have a lathe and some generic tooling and some metal and skill, you can make this yourself. You will then need a mill and a rotary table to get the holes in the hubs concentric. making this part by hand will be difficult and time consuming.
Overally i personally would not re-invent the wheel (pun intended). I would shop around an find a design that fits your needs that you can get to work. If you are making a scooter do you want it to coast? Direct drive may not be good for coasting.