Dude first of all for a drone to fly properly it should be balanced and symmetric or it will go down. Then for the drone to be able to deliver the pizza you will need gps module for arduino which will provide the coordinates to where the pizza should be delivered.
Then to send the coordinates to your drone you can use bt module and an app that can be made from mit app inventer 2 there are youtube lessons also search for it then an ultrasonic sensor to maintain the height of your drone it will be flying at.
And you can program it such that when it reaches the desired destination it should lower it height which can be done by programming in such a way to lower the motor speed. to reach a lower height.
And for the code i dont seem to understand what help do you need in it.