DBC's exes (in version 1.20) always start out at about 1.7 megs + the size of your .DBA file and .DBA libraries. You can get a rough aproximation of the final size by adding the size of your .dba program and libraries used and the size of any media you uses. So if all your .dba files were .5 megs, your images added up to 3 megs, all your sound was 20 megs, and all of your models were 10 megs, you could guess the size of your final exe in DBC to be about
exe start size (1.7 + .5) = 2.25 megs
media = 3 + 20 + 10 = 33 megs
a final exe build = 35.25 megs
Of course, you could just build the exe @ 2.25 (not a final that includes media built in)
and store your media compressed so the final distribution is smaller.
If you use build final, your directory should be clear of everything except what you want included in the final build. If there are any "extra" test files, or exes, or whatever, they can get built into your exe; bloating it's size and possible making it not work.
Enjoy your day.