My pool was built in 1978 with concrete blocks, vinyl liner, and a sand bottom and it is still holding up fine today. It also has concrete poured down into the center of the blocks. Two walls are 8" block and the other are 12" block. They had planned on making it an indoor pool someday so the extra 4" is for a outside wall. It's had 3 liners.

I had a friend that built one with the treated plywood. It lasted about 10 years and then the liner failed. They were tired of it at that point and filled it in. Wasn't very expensive to build and it was a lot cheaper to fill in since it didn't have as much concrete.

If I was going to build one today I would go with the polymer wall vinyl liner pool kit with a sand bottom. To me the sand bottom is very forgiving if it happens to shift any...I live in a area that has earthquakes on occasions and they tell us we are going to have a big one in the near future