Building a small extension - Drainage?

We have a single skin utlity room attached to our house that we are looking incorportating into our house in the furture. I have had a brief chat to building control, and think I have agreement in principle from them on how I would upgrade the walls.
The roof is currently 10mm double skin poly, and I would like to remove this, replace with a single pitch tiled roof and add roof lights.

While thinking about doing this, we have thought about extending the utility room, as it does not run the full width of the house. It would only be a small extension (about 1.9m x 2.1m).
The problem is that there is a gulley just outside the back door that I would need to build over. It picks up the water from the roof, but this would change if we building on and the waste water from the bathroom.

So my questions are:
1. Could this be connected to the soil waste pipe?
2. Is there standard way of building over/close this gully?

Thanks