Making my own cross stitch pattern?

Hi! I’d like to make a cross stitch of a saying and have never made my own pattern before. Many years ago I did counted cross stitch kits and would like to pick the hobby up again.

How do you go about creating a design? I know graph paper is involved, but where can I find templates for letters and that sort of thing? Is that even how it works? The saying is pretty long (40 words) so I’d also need to figure out how much space and materials are needed, too.

Any advice is appreciated! Thank you.