I am building a shed. its all framed. Shed style roof 2x6 rafters 24 oc. with 2x4 purlins spaced 24 o.c. over them. So my question is how to seal that top lip so water doesn't run down the underside of the roof. Is there a drip edge or flashing that attaches over the top of the roof and to the front facia (which isnt up )???