I really like Zalo's mod that gives you cash when you kill someone and i love to play with single character against a horde of enemies.

I would really like a mod that allows you to buy a possibility to buy a building.
An Example:
I start a game with a single Brain Character,a gun and 0 cash.
I kill some enemies and get some cash.
I order some kind of special Lua'd actor that allows me to buy single module or item from "at the start buy menu" and the destroys

That way i can progress from single character to a base and feel that i have archieved something

Can't be done in any way in the current build and possibly not in the future.

Method 1 of calling up the buy menu is going to lag horrifically because you're not supposed to be able to do so once a game starts.

Method 2 of creating an instantly-settling bunkermodule also would not work because of IsScrap, which causes settled MOs to become ludicrously destructible.

Search "Scrap Brain" for horribly laggy base building mid-game.

I know that Ballistic Weapons mod have a build module and if you drop a bomb in it you will be able to build without any lags. (or i didn't notice any lag.)

Then post the code and request that someone Lua literate put it into a .lua file for an actor.

Going back into bunker-build mode is something that has to be done once every sim update; it can't be done by mods in a regular skirmish game without quite literally reopening the menu every single frame while the game is trying it's damnedest to reload.

That's why it lags.