ALL CREDITS GOES TO - Sirhc(Youtube).
So if you ask, what have I done? Well I've just recreated the entire main structure which people feel extremely annoying to build especially dealing with waters and hostiles ,in creative mode, and I've made it a bit more aesthetic. AFAIK there is no such a design post here till now.
THIS FARM IS NOT FUNCTIONAL!! (It is the main part). To make this farm functional:
1 - You NEED TO FIND AN OCEAN MONUMENT and REMOVE ALL BLOCKS in an 64X64X26 area from the sea level, around and include the monument.
2 - ALIGN THE CENTER of my schematic with the center of the monument (the edge of my farm shall be 3 blocks away from the edge of the monument).
3 - Make sure 'Without air' and 'With water' are selected in the import selections, and paste it.
4 - You NEED TO COMPLETE THE TUBE where guardians fall, known as, the killing part.
Please do consider my farm no more than a gathering device. I think it shall be easy after all I've mentioned above is done.
After that you may need to clear some gravel/stone at the bottom layer. The Falling height needed to kill a guardian is 34 blocks I believe, which means you may need sth like lava or the cactus trick, to shorten the fall, just for eg. Sure you can also use this as a normal mob farm with all sea-lanterns and glass replaced, and it will have a decent spawn rate.
At last, thanks to Sirhc again, and may all enjoy your games and have fun farming those crazy laser-shooting bastards!