Okay, I am thinking of Calamity Single player. Here is what I think it should be like:

just like the multiplayer, but it would have a bigger game space and more stuff. This game shpuld be started when Calamity multiplayer is finished.

The game would contain levels, enemies with different guns, explosives, maybe knifes etc. Every mission would give a certain amount of money with you can buy weapons or armour. Some missions would contain C4 explosives or something like that, you get it for free but only for that mission. There would be a list of missions from easy to hard. The game would contain bunkers and buildings. Some of the missions would require a special gun (you can do the mission only with that gun).

This is a shortly made idea, I want to see what you think. Is it too hard, possible, any opinion is appriciated.

This isn't a bad idea, I would definitely consider doing this. I think it would make for a good game. But as of now I haven't made a game with a lot of levels and a story line, so it should be interesting.

This is a good idea, But make a multiplayer.

This is a good idea, But make a multiplayer.

I can't be making everything multiplayer, there's only so much I can do.

If you make multiplayer, That is your hardest thing to do.

Making a game is relatively easy, but adding multiplayer takes it to the next level. Depending on the type of game you make depends on how hard it is to code the multiplayer. I have to send information from the peers(People playing the game) to the host(Person hosting the game) then the host has to send the information back to every peer. So if there are 2 peers, they each send 1 piece of information to the host then they're given 2 pieces back; 1. there original information but in executable form rather than variables, 2. The other peers information but only in variable form. Then afterwards the peers send the variable forms to the host again and the cycle repeats. This way everyone is sent everyone else's information and it is displayed on the screen. Causing multiplayer.
This was only explained very briefly, I might do a better explanation some other time.

I understand.

I would hope so.