you are referring to the current ASIC USB miners??
your question isnt as silly as it sounds although that would depend on your knowledge of electronics.
with globalisation these days it isnt so silly to ask. i would say the 2 stumbling blocks would be programming of the chips and creation of the pcb.
everything else in my experience would be a breeze such as assembly. testing however, if you dont have a golden board to reference would be hit and miss.
global supply chains these days are amazing.
seriously though, if you know how to obtain/ get around the 2 issues as above please PM me i would be very keen to make my own.
hell, you have almost inspired me to buy one online and reverse engineer it. really doesnt seem much to them, initially.