I create a custom domain refer here
https://help.directadmin.com/item.php?id=199
|*if SUB="subname"|
|?SDOCROOT=`HOME`/domains/`DOMAIN`/subdomains/`SUB`|
|*endif|
Good here, but the problem is with php still pointing to main docroot
<Directory /home/user/domains/domain.com/public_html>...