We have just had bifolds installed as part of an ongoing self build renovation. The next part was to try and create a possible seamless threshold from external patio to the inside. The cill sits on one brick above dpc and two bricks away from current patio. It has been suggested bitumen paint on the brick under the cill and an aco drain from the cill with slabs obviously falling away from the house and a French drain as such under the cill.I’ve read a lot of similar threads on here and thought could it be this simple? Property north facing and is protected from most rain. Attached some pics which may help. Appreciate any observations or suggestions