Can I build a 8x12 deck for above ground pool out of 2x4s?

Sure. It's done all the time. Just make sure you have plenty of braces under the 2by4's so it won't be 'bouncy' when you walk on it.

All pool liners need replacing some time, and yours will too.So maybe instead of an all-around deck, maybe try a half-circle; it may not look like an in-ground pool, but, hey, t's better than tearing the deck apart in a few years. Good luck!! <3

The inexperienced woodworker and the very experienced person will be able to do these projects without any difficulty https://tr.im/bBRyZ

Each and every one of the thousands woodworking plans and projects which are available are so well written so that even if you've never tried Woodworking before, or if you have 2 left hands, you would find woodworking a breeze

You can plank with 2 x 4s if you want, but for an 8' span

you will span need 2 x 8" rafters on 16" centers minimum.

Check local Codes. It needs approved plans & inspection Y'know.

You don't get to decide the load rating. It's a matter of local law.

you can but you should not

Yes you can