To build a custom AR-15, you need a lot of patience, and in fact, perseverance is the key. Please start with the receiver as it is the home to all the gun components. Always remember that you have to register the element with the federal department before you use it. If you don't have the proper paperwork, then it will be considered as an eighty percent or unfinished receiver. Civilians refer to them as ghost guns because it is difficult to identify them accurately.