John Deere 6920 Front image - TractorSource Mod for Half-Life 2

The basic concept is going to be this. You're a farmer and you start of with just enough credits to buy a tractor with some equipment. You mow the field and turn the remains into blocks. Then you transport these blocks to a storage bunker and from there you can put them into an oven of sorts. The blocks are now transformed and using a forklift you can load them onto a trailer. With that trailer you'll transport these blocks to a refinery and for each block you deliver you get one credit. So basically the more blocks you take to the refinery the more credits you'll have and you'll then be able to buy better and faster machines.