Soldato
Is it a vinyl or mohair roof?
If vinyl then AG vinyl and rubber care does a great job : http://www.autoglym.com/products/products/vinyl-and-rubber-care
If mohair then GTechniq I1 is hard to beat http://www.theultimatefinish.co.uk/gtechniq/i1-smartfabric-coat-500ml.aspx
Was just about to post and recommend the Gtechniq stuff - it really is awesome stuff and allows the rain to bead on my roof same as it does on the paintwork now