Next, you will need to determine the type of key switches you want inside of your keyboard. There are countless types you can go with, but the most popular brand is called Cherry. The following link gives a good breakdown of what the different switches feel like, but I would recommend you try out the switches before you buy.

https://www.gamingfactors.com/mechanical-keyboard-switches/ 

Once you have both the layout and switches picked out, you are ready to start building.