Sloping floor and real wood flooring

[orinoco]

We had an extension built on the front of the house which has made the hall bigger but the builder has left a level difference at the point the old wall has been taken down. Overall it is about 8mm and a slope from new to old. Levelling compound will not work as it would make the floor too high in the old part. Is the a way of laying over a slope? Glue down the wood I suppose but real wood will not flex enough over the slope to do it.