THANKYOU ALL for advices. What I did, since I couldn't find any help or any other shop with this specific experience in my town, I hired a carpenter, and together we created a type of metal "L" for holdign the sign, just screwing to the beams, not touching the roof, and in the lower part, we attached to the concrete wall with metal "L's". It is very strong though, due to the fact that in this town (Spring Valley NY), wind is strong, and village rules are kind of hard, but it kept really good. I appreciate everbody's comment.