[updated:LAST EDITED ON 15-May-02 AT 07:54 AM (GMT)]First question is why do you want to use a Offset dish of this size ?
Offset dishes from Channel Master are available for 1.2mtr 1.8mtr and 2.4 mtr dishes.
The mount for a flat roof is dependent upon the constuction of the building.There are special mounts from such as KTI that allow you to place blocks on the mount to act as ballast and prevent movement. Check out the KTI site for futher information
But normally you would have a structual engineer design the fixings bolts etc - do not do this yourself i would suggest!
what signals are you looking to recieve and what is your current location.
Prodelin manufacture a 1.8m receive only dish, their advantage over the Channel Master is the polarmount as standard so motorising is easy to achieve.
Why the need for an offset dish? The 2.4m from Prodelin is a prime focus dish but once again it has a polarmount
I agree that in an install of this nature it is best to check with a structural engineer on both wind loading and amount of concrete necessary to hold the thing down. Additionally it is strongly advised to chain all parts to secure them from sliding across the roof in the winter.
Just thought to add that should you have access to trade business cards then you may be able to purchase the dish from
www.doebis.com for poss 40-50% less than normal UK prices they are based in Germany - near franfurt - they carry a large range of large dishes upto 3.7 mtr in stock. including IRTE prime focus and channel Master etc. They also have H-H and Polor mounts in stock for dishes upto 3.7 mtr