20x20 RGB LED Matrix controller project
Well, I would be tempted to use 4 of this small matrix for a 16x16 (around 12cmX12cm) or 9 for a 24X24(around 18cmX18cm) matrix, they are controlled using SPI, so an arduino would be able to control them and use the arduino wifi shield for you wifi need. It might not be the cheapest solution but its probably one of the easiest and fastest you can find