A few other tips:
-dig sheer walls not slopes, this is a heron deterrent and also minimizes jumping risk
-do include some type of egress (steps, etc) for pets or kids in case of accidental entry, the liner when algae covered is extremely slick
-gently slope the bottom though toward the center
-have a centered bottom drain feed to your filter, this is more work initially but will save thousands of hours (and $) later
-dont fill the bottom with gravel, this is a pain to clean and will trap detritus - and you WILL have pea soup for water in no time
-build large as you can, just like a reef you never end up saying I wish I had a smaller pond
-think carefully about filtration (hints: surface skimmer, UV) dont think you're just digging a hole the ground and nature will take care of it...