Snowball's major idea for improving the conditions on Animal Farm is to build a windmill. He proposes this idea in Chapter V.
Snowball argues that building a windmill will improve the lives of all the animals. He says that with the windmill they will no longer have to work any more than 3 days per week. He says that the windmill will generate electricity that will allow the animals to have warm stalls.
Napoleon is totally opposed to the idea of having a windmill. When Snowball speaks in favor of the idea, Napoleon has him chased from the farm.