[Self Drafted] Minecraft dirt block bean bag – advice n Sewing Machines Parts and Sales in Los Angeles

So, my SO and I are moving into a big new place, which means that my step son will have his own new room now. I want to make him something nice for his room. He’s 11 and a fan of Minecraft. I was thinking about making him a dirt block bean bag to sit on. I saw this guy’s work and I love it http://jack-norris.blogspot.de/2012/07/minecraft-dirt-block-poof.html

So I want to make something like that, only larger. Same plush/grassy top, but with this fabric from Spoonflower instead of gluing fabric bits on the base. http://www.spoonflower.com/fabric/4646961
I feel confident enough to make my own pattern, but I do have some concerns and questions:

1. Is a cube shaped bean bag a good idea in terms of comfort and appearance, and how big should it be? Is my project feasible or should I strive to make a stool/footrest instead of a bean bag?

2. Is Heavy Cotton Twill or Eco Canvas ok? Can I also use a lighter fabric?

3. Is the carpet top a good idea or will it be a total pain to work with?

I’m a fairly novice seamstress, never tackled a bean bag before, but I love a challenge. Since this fabric is expensive (I usually go for as cheap as I can get) I want to make sure my project is feasible and will produce a decent result. Advice from more experienced members appreciated. =)