Well, you basically should decide out right. Do you want to build a loop, or not?
I am a massive proponent of water cooling your system. But being said it really is not for everyone as there is both, reward, and maintenance along with a substantial cost increase. Expect to spend $400USD minimum to do a liquid cooling setup correctly from scratch with any quality parts at all, and it only goes up from there.
If you chase a mid tower computer format, and you do decide to build a loop later, it will require much greater part planning than just outright buying a larger case designed for water cooling. As space becomes premium, and radiator thickness, res size, bend radius, etc all become more constricting factors. I tend to believe midsize builds look better than large case builds anyways, but I also perform these builds and can tell you they aren't as simple as my large builds have been as parts become harder to pick from.
The fact that you chose a 800D originally tells me you likely do not care for all the ugly flare and flashy cases out there (maybe I'm wrong), fortunately for you there are many cases being made now that do not have all the fluff, It used to be a boring case or Lian Li for a nice refined build if you didn't like tacticool plastic and steel. Take a look at Fractal Design (Cheaper and All Around Good), Lian Li (Unparalleled Modularity and Clean builds), Be Quiet! (Amazing Quiet Cases that do it all) for mid tower cases that can act as Air and or Water, while not looking like a heap of (s)crap parts trying to serve a purpose.