Walkthroughs for custom maps.

We've identified areas with boxes, and it won't be possible to accumulate an army; the map will penalize you for that.

Could you rephrase or explain this sentence? I didn't understand what you meant by "areas with boxes" (I haven't played this map).
I'm currently playing a map that was previously reviewed here, and after finishing it, I want to add my thoughts and some useful information for others who might want to play it but encounter difficulties.