We would like to draft a letter to inform customers that we cannot provide services to them. I would like it to be short and to the point but yet in a very polite and professional manner.
Below is what i came up with so far... Do you think this is adequate enough?

We regret to inform you that we are not able to provide roofing services to you at this time. Thank you for considering us, and we apologize for any inconvenience this may cause you.
Hi, welcome to the forums..

That sounds fine tropical; short, to the point and polite! "apologise" with an "s", unless you want the American spelling.
I would change "not able" to "unable," since it is shorter and therefore more fun.