Rather depends on the material of the roof, if asbestos or corrigated roof sheeting then the best way to seal it will be with a roofing mastic , just be carefull! these roofs are fragile. if it is a timber deck roof with three layer built up felt there are roof paints available on the market, d.i.y retailers or roofing suppliers can sell you any of these. they are all about the same, just avoid water soluble ones. or you could be brave and buy some torch on felt a roofing supplier, £30 for 10mtrs though. if the leak is small and you know where it is a normal small blow lamp will warm it enough to melt it on.
make sure its a dry day and you clean area to seal, ie stones durt etc for any of the above methods.
have fun.
jay, October 2008
