I'm charged with the task of designing an invoice. My requirements say it has to have multiple blocks per month and inside each of these blocks, the cancellation part has to be divided from the corrected calculation. Also, we need subtotals for each of these blocks (have a look at my mockup). To make things worse, there can even be intermediate totals between the positions.
The invoice is a PDF document which will later be printed out. Please don't care too much about wording - it's not english anyway.
So, my question is: how can I best depict this structure of hierarchical blocks? I know there's not the perfect solution, I'm rather looking for different ways of designing these blocks. They should be easily distinguishable and not hurt the eye (like my mockup does).
I would like to stick to my font and use two sizes maximum. I need to use black and white only - some gray would be ok, but I guess it can't take more than one shade of gray. I'd like to cut down on the lines (in large quantity they're more disturbing than helpful).
Do you have some ideas or hints for designing these blocks?