why you not start by built you own flapy bird or candy crush, get money, and use that money to hire professional for working for your game:)
for your question, I think you will have (atleast) this 5 problem, but easy to solved (by yourself)
- 3D assets
problem is, that big city need a lot assets to make from basic cube into textured building.
easy to solved if you already have a lot assets, spend your time to make all of them, or have money to buy from assets market. - In engine work.
problem is when you jump to setting all material, lighting, technical aspect, how to make level run smoothly (you must spend much time for it)
easy to solved if you hard worker person
- Hardware
that big city need high-end hardware, open land with deer, rocks, forest (Kite open demo) is small example for hardware requirement
easy to solved if you already have super power hardware
- Time (I know you know what I mean)
- Desperate
you know this problem, every one always have this problem its hard to solved, and its always come suddenly
people (included me)says that impossible because your picture come from top-front view that covering all 3d assets on that level, of course its hard… If I remember correctly in EPIC GDC “Making of Paragon” there is discussion about LOD, if you can play with LOD I think it will possible to make that city (city from first image) or do programming magic (destroy all interior or assets that will not shown in scene, and load them all when it needed)
from you pictures, its come from FF XV right?
first images, I believe its reachable in UE4
but for second image, (I guess that from CGI movie of FF XV Kingsglaive trailer) I believe its come from pre-rendered CGI, with big high end render farm.
but if you use super-ultimate-ultra low poly assets, non dynamic lighting, I think you can make similar level like that (come on, its just super far camera view, no need to get detail for it, just use simple cube with building texture, and you’re done, load the “gameplay level detail” when camera become closer (LOD thing)
If you are programmer, don’t forget, EPIC give us source code of UE4, you can play with it to make your own “RAGE engine” haha (I dont know but your question make me thinking about this awesome Rockstar engine)
I recommended you to watching EPIC GDC event, both of “Making of Kite open world demo and PARAGON”
and don’t give up, even other people say its “impossible”, put that “desperate word” into your motivation