need help with an rfid

i want to build 1 from scratch, the tags i have are 13.56 mhz and want about 5ft of range so that as i walk upto my door the scanner reads the tag and unlocks the door

For that sort of range you need a device that transmits on one frequency and receives on another.

It can be with a passive tag such as done by this https://focus.ti.com/lit/ds/symlink/ri-stu-251b-01.pdf

Most car keys that don't need to have a button pressed have a battery and they respond in the same way as the car keys that do have a button to press.

Single frequency passive systems aren't going to get much more than 0.5 m.