Waterproofing

This might make some sense if rain only fell perfectly perpendicular to the surface of the earth. Since wind swept rain can move virtually if not briefly truly parallel to the earth I believe a roof overhang will not make a brick wall more or less waterproof. I do believe though that the amount of overhang can be a significant cooling advantage in your region by shading your brick walls.

Yes, this will help. In the US this is called an eave. Bear in mind though, when it rains, and the water runs off the edge of your roof slab, it can collect as drops underneath and find it's way between the slab and the brick wall.

In addition to the overlap, you may want to include some type of mastic between the slab and the wall, or apply a urethane caulking to the remaining small gap on the outside between the slab and wall. This will insure that water runs down the outside.........not inside.

The overhang is good but it needs a rain drip, a groove on the underside. The best illustration I can find is in the front of this Bathouse.

That's a good idea.........................as long as I'm not the guy that has to cut the groove on the bottom of the concrete slab.

Just to add to your thought, maybe set a channel in the concrete slab when it's poured.

That was what I had in mind, the overhang has to be formed, he could nail a 1/2 inch square or quarter circle to the form, perhaps an inch in from the edge.

This is all well and good and more than likely what the OP originally meant to ask but isn't the use of an eave with a drip ridge a weatherproofing technique and not a waterproofing technique?

There is a well proven old time waterproofing method good for a year or two per application. It is also letting it breath: letting vapor escape. Trapped vapor is a cause of wet walls.

It is Whitewash, made by slaking burnt lime in water, then painting the wall with it.

It adheres to brick and concrete fine. You will find old fashioned tradesmen to do the task.

A true concrete house is probably more waterproof than any other common type of structure and only cracks, joints, or window and door openings should require attention.

if the brick. and mortar were layed by a compentent contractor, there's no need for an overhang. it would be ineffective

Concrete slab should be poured in one pour. Construction joints will increase risk of leakage. Waterproof with a suitable paint on memebrane. Overhang will protect the interface of wall with the slab.

Drip grove must be tapered, a square mould will get stuck in the concrete and make it very difficult to remove during stripping.