For a long time now, I have been using premade grid systems, like foundation grid for instance, which consists a grid of 12 70px columns, and 30 px gutters. But as my design passion seeks the best possible harmony and proportions, I'd like to build my grid more adequate to the specific project needs.
What base unit should i start my calculations with?
Should i use base line height, main typeface x-height, or maybe some other significant value? I've read more meaningful typography article on A List Apart by Tim Brown, but he suggests basing it on font size, but as Erik Spiekermann pointed out, real font size depends on it's family.
For myself, x-height makes sense, as it's affects the visual space and weight of layout a lot. But on the other side, line height sets the vertical rhythm.
When I've got the unit, how to decide on column and gutter width?
Giving that i can choose out column number constraint (depending on the content complexity, or maybe i should concider other factors as well?), I still need to decide on website max-width, gutter and column width.