The plastic and vinyl liners have an average warranty of 10 or 15 years while the 45 mil. If you have to skimp any where on your pond don't start with the liner. The next job was was to layout my garden on paper starting with the shape and location of the pond. A word on shape. Like a flower bed stay away from round or square shapes.
Odd shapes are more appealing and more natural looking.
The biggest chore for us, because of our level garden, was to build a slope for the stream as if it were flowing down a natural hillside. This was done with about 15 pickup loads of rock spread across one side of the garden and shaped to a gentle slope. With the slope completed I now had the exact location of the pond in mind and marked it with rope. Six pegs were driven around the pond about one foot outside the perimeter. Using a straightedge and level they were driven to a point where all 6 were the same height, approx.