I often find that the border type I like to use doesn't exist. The lines are 
either too thick or too thin. I can define my own colours, and I also want to 
define my own borders in just about the same way.

Parameters I need to adjust (at least):
Single/double lines selection.

Outer line (or maybe "left line" or "upper line"):
     Thickness
     Line style (such as continous line, fine dashed line, dotted line etc)
     Colour
     Etc...

Inner line (or maybe "right line" or "lower line"), only when double lines are 
selected:
     Thickness
     Line style (such as continous line, fine dashed line, dotted line etc)
     Colour
     Etc...

Distance between inner and outer line (when double lines are selected).

Line alignment selection:
     Outside cell 
     Inside cell
     Half inside and half outside cell ("center")
          Example: The cells itself is 5×20 mm. Total thickness of
          singel or double lines are 1 mm. This line style is
          selected for all sides of the cell.
          Selecting "Outside cell" now makes the cell look like
          7×22 mm, making surrounding cells look smaller. Selecting
          "Inside cell" makes the cell to still look like 5×20 mm
          and surrounding cells are not affected. Finally, the
          "center" option makes the cell look like 6×21 mm,
          affecting surrounding cells with only half of the total
          line thickness.

Name of border style

Well, feel free to add more parameters to this list...

Johnny