Does anyone know an up-to-date tutorial about how to make something like a chest but with less spaces or a chest with more spaces?

yes... thats not hard at all

 

All you need to do is to create an block which extends blockContainer,

create a TileEntity for that block and a GUI class for that TileEntity/Container.

It's rather easy and mostly copy-paste existing code from minecraft classes

 

On the forge wiki there are some tutorials for GUI's have you read this one?

http://www.minecraftforge.net/wiki/Containers_and_GUIs

 

 

yes... thats not hard at all

 

All you need to do is to create an block which extends blockContainer,

create a TileEntity for that block and a GUI class for that TileEntity/Container.

It's rather easy and mostly copy-paste existing code from minecraft classes

 

On the forge wiki there are some tutorials for GUI's have you read this one?

http://www.minecraftforge.net/wiki/Containers_and_GUIs

That was helpful I didn't realize that tutorial was updated. This is a really noob question: How do you create a TileEntity that implements IInventory?

 

EDIT: Nevermind. How do I exactly make a GUI image for exactly that inventory?

How do you create a TileEntity that implements IInventory?

class TileEntitySomethingClever extends TileEntity implements IInventory.

 

EDIT: Nevermind. How do I exactly make a GUI image for exactly that inventory?

Well you have to create one inn paint or gimp or photoshop etc.

What I did for mine was to go into PS and just copy paste and move around stuff from the original GUI's

You can find the original GUI images inn the

"mcp_Directory\temp\bin\minecraft\gui"

 

And use them as a starting point

The images Demo_bg, slot, Container and  should give you some good starting images.