Hi
I do not have much experience with creating or developing online or multiplayer games but i was wondering if it would be harder to implement online features on an offline/single player game that is finished as an update or do you actually need to start a new project and start with a multiplayer features in mind?
So is it really harder to implement online after a single player game is done?
Thank you in advance for helping me out 
There is no way to really answer this accurately without knowing more about the type of gameplay.
But lets just say its a big ask to bolt-on multiplayer later (if you only knew all the voodoo involved).
If its a fast paced shooter game etc, just managing to accurately gauge head-shots is an Art-form…
And if the game maps are huge, you’re also into Origin-Rebasing both on Client-side + Server-side.
To sum up, the gap between a simple mp card-game vs MMO, is like Homer Simpson vs Einstein. 
There’s some really good reads out there, early Source / Doom blogs. Gamasutra ran a series too…
@ClavosTech thank you for your reply.
I do understand that the type of gameplay decides everything but adding an online feature is perfectly possible without the need to rebuild the whole game?
Without knowing more about the game there’s no way to know reliably tbh.
Suggestion:
On the Play menu, set number of players to 3 (leave dedicated server off)
Watch closely what works, and what’s instantly broken to get some ideas.
Is everything working in the Listen Server window, how about the Clients?
Rebuilding the whole game? It should be easier if you can leverage the CMC.
But if a game has lots of CMC customization its harder, see TheJamsh posts.
A card game / slow moving Homeland strategy space shooter may be easier.
The blogs above explain why multiplayer is tricky, the biggest issue is Lag etc.
Hello @TsurutaProd
Retrofitting networking is way more work, but it can be done. I’ve purchased several BP packages from the marketplace I had to retrofit. Way more work then I bargained for. As you’ll have to re-engineer the code base to implement replication features in specific Classes at the function and variable level. Now I only purchase BP packages that are Network-ready. My personal recommendation is implement networking upfront for ALL features for greater flexibility in multiplayer. The Single player option always exists by default.
UE4 Networking References: Videos
https://www.youtube.com/playlist?lis…SFPRiBpwe5sTwc
https://youtu.be/U1LwGHynZhw?list=PL…JGfSvgevcuI4Pi
https://youtu.be/z7DI17JAGQM https://youtu.be/hDRoglljXjohttps://youtube.com/watch?v=J0bLy3AVJt4
Documents
https://docs.unrealengine.com/en-us/Gameplay/Networking
http://cedric-neukirchen.net/Downloa…Neukirchen.pdf
https://docs.google.com/presentation…it?usp=sharing
Thank you so much @TechLord and @ClavosTech for the information you both provided! I really appreciate it! :D:D