subdomain or root directory

[saytouqeer]

hello to all
I want to make a community forum of my website and I want to promote the services which I have provided.
My question is that making a forum on the sub domain or root directory of the url of my website.
Which one is Good for crawling and Indexing of the Google.

 

[saytouqeer]

too much time no body is apply for this threat. How should I resolve this problem?