How about that:

You drop a rectangular shape onto the editing box. it will autmaticly snap to near regions (or borders) but you should be still able to fine tune it and choos NOT to snap. maybe you want to have one small window in each edge of the screen, so you can still have another program in the middle.

Maybe with left-clicking into the area and getting a textbox which shows the exact values


to make it a lot simpler, you could add some predefined-layouts, or add an mechanism to save a layout in a file (for further use - or for sharing)

(in the end, its nearly the same, which you have already implemente. but with some changes. making the vertices movable, and making the lines movable....)


So you have:
- comfortable setting the regions through simple clicks
- ability for finetuning "per pixel"
- ability to save you "hard work" (especially if you have multiple setups (dual-box & 5-box for instance)
- ability to have a "Newbie" not to mess up with the editor, beeing able to choose a predefined set, he likes to use.