You could use Lamassu's open source Bitcoin ATM software that way you wouldn't need to dev all the software yourself. However its not that easy to find hardware that will work with the Lamassu OS.
So far as building your own software, that's probably a lot larger project than you really want to get into.
Point. Unless you plan on distributing your own version of this ATM in a "leasing" manner like Lamassu does, it may be cheaper to just lease/purchase a ATM from a known company.