Glad the pool is almost completed. What did he go with as far as returns, skimmers, and main drain? If I were building a pool I wouldn't use a main drain. Too many problems reported on this forum over the years. What I would do is rig a suction line just below water level where I could hook a hose to it to suck from some contraption I could put on the bottom of the deep end. Leave it in when the pool is not in use, remove it when in use if it's in the way. Would be a removable main drain. No penetrations, no possibility of leaks, no complications.
Hope the winter is short.
Al