There are several "Pond" threads on the forum so it may be worth your while to have a look and see how what others have done.
On a personal level, I undertook a similar project some years ago.
Neighbour with a mini digger scooped out a large hole in the middle of the paddock. I used the spoil to bank up the sides and create some shelves. The finished dimensions were approx 7 mts x 4 mts with a depth varying from 1 to 1.5 mts.
I used a layer of sand to cover any stones, etc. before laying the liner - Butyl in this case but there are cheaper alternatives. You can also use a sort of soft woven underlay instead of sand. I've used this in my current pond with no problems.
I started the pond in Spring and spent the following 12 months planting up around the pond and establishing the aquatic plants.
The wildlife moved in pretty smartish and by the 2nd year, the pond looked as if it had always been there. It was hard work at times but immensely satisfying.
I wish you luck and hope your OH enjoys his extremely generous Christmas present