I'm developing a game with quite a rich story. I'm not sure if I'll have enough time or money to make a level for each part of this story.
Is there a common method among designer to manage this problem ? Should I write the entire story first and then cut some parts to fit it in my time/money budget ?
I think you pretty much answered your own question there yeah. Depending on how important the story is to the game and especially the gameplay, you write the entire thing first, then cut out the things that are least relevant until you have something you CAN do. Or if you know what you're doing, you drop stuff before you even write it.
If you're making a game where the main focus is the story, however, I wouldn't recommend it, as the game is pretty much just a vessel for the story. In that case you want as much of the story as possible. This is the case in visual novels for example.
tl;dr: Really critically think for yourself how important the story is to your game as a whole, then decide if you should cut parts, or leave it.
You could also (if possible) split up the game into episodes like how Telltale approaches their games and continue development with the funds you gain from that.
One important piece of advice I would like to give you, write the beginning and ending first. Make those two things the best parts of your story. Then the players will be enticed by the beginning to continue and satisfied at the end because of the good ending. If you run out of time while writing the stuff in-between, that's fine, you can still link it up.
The "design first, cut later" principle can be fun at first because it doesn't impede creativity too much with concerns of what you can realize. But it leads to frustration later when you realize just how much you have to cut to stay within your budget. The result might be just an empty husk of your ambitious original idea which lacks everything which was interesting about it.
But you can of course also approach the problem from the other side. Eyeball what content you can create with your resources, and then think of a game concept which can be realized with that amount and quality of content. This might seem restrictive, but those restrictions can also be creative fuel. When you try to solve design problems with minimal resources, you might come up with unique design solutions the AAA studios would never consider.
When you have a small budget, then you can't compete with mainstream games on quality or quantity of your content. Your only hope is to be unique. And a lot of unique design solutions can result from having to work with what you got.
One approach is to go with at it in a hierarchical fashion.
Write a simple outline for the whole story. Put only the important stuff, the things that affect the rest.
Then, dig down into one part of it. Flesh out one level for this part. This will force you do design the settings, the characters, the motivations, what happened before that you must state, what might happen later that you allude to. A prototype there will/may convince you/inverstors that the whole is of interest.
Then just go back to the high-level story, improve it a bit, and budget allowing, dig down into another part.
That way, you avoid useless work, you remain agile, allowing you to adapt to inevitable discoveries (this character doesn't work, I need this type of location/setting, people would rather see xyz).
Best of luck with the project!
