This question is applicable to internal walls - for external walls, the doors generally come in a frame and, with the cavity wall, the situation is a different kettle of fish.
The width of the linings should be calculated to accomodate the block wall and the thickness of either the drylining & plaster or render and plaster. So, the plaster will be skimmed flush with the surface of the lining. The architrave will then then sit nicely across the lining and plaster.
Your architect should have provided the dimensions to provide for the surface area of the roof. You will need also to take into account any paved areas around the house which drain into the system.
The essence of a soakaway is a pit, filled with clean stone, into which the surface water discharges, and from where it then percolates into the surrounding ground. A clay soil, or a high watertable are not good for a soakaway.For some photos of the preparation of a simple soakaway follow this link to our Build Process photo gallery