directadmin directory structure

Im trying to get my head round the directadmin directory structure.

the customapache directory - why are some programs installed in here and some installed in usr/local?

are there certain programs that I should install/upgrade in customapache and all others go in var/local?

why do I have httpd in the customapache folder and also in /usr/local/apache2/bin?

is there any documentation on this? I have looked in the knowledgebase and other places, but have not found anything about this specifically.

customapache is just containing the source for compiling.....

well thats nice and simple so i take it i can safely delete stuff in there then?

yes, or just type

./build clean

to clean the source.