This post will dig into the tools and techniques for both creating custom fonts/characters on the Commodore 64, then using them in your BASIC programs.
The Commodore character editor I currently use is called Character Editor 2.
A quick look at the .d64 disk image will reveal a number of f.filename entries which are character sets already created.
I've included a small program on the disk image called: BASICLOADER which will allow you to load these character sets into BASIC without it interfering with BASIC itself. This program can be easily adapted to load the font on program startup.
Exchange line 10 with A$="f.filename" and include the character set file on your disk to allow your program to load the new characters at program startup.