I don't know what kind of implementation for this you need, however here's a three-line bash script that would do just that (at least in gnu-linux).
MOTHERPERM=`stat -c %a $MOTHERDIR`
mkdir -m $MOTHERPERM $1
So i.e. you could put this in a file called /usr/bin/mkdir2, chmod +x /usr/bin/mkdir2; and then create your directories using 'mkdir2 /absolute/path/of/new/directory'