Need help with this idea please?

I'm wanting to crochet just a simple afghan. I have two colors, spring green and sky blue. I'm thinking of just making blocks, starting by chaining 10, i don't know how big that would be. I will also be using a size J hook. I just need feedback, opinions, ideas, anything at all will be helpful. Sorry I don't have much information, I'm just not sure what I want to do. :)