building my own cage?

My dad and I have decided that the piggies need a bigger cage. I'm not sure yet where I'll put it, but I'm thinking on a table in my room (or on the floor..who knows??) I'll admit, I don't know a whole lot about guinea pigs. Well, I know how to take care of them and feed them, but when it comes to what they need cage-wise, I'm a total newbie.

Since we're building it we're free to put pretty much whatever we want into it :] I'm really excited about that..but I don't know what to put in it.

Their cage now seems a little tiny (probably okay for them but whatever) so I definitely want it to be bigger, so I know it will be bigger..but how big is roomy enough for two guinea pigs? Is it okay if the cage is long and kinda skinny? Or should it be more square?

My dad's pretty good with making things (we built me a saddle rack earlier this year) but we need plans.

Should piggies have multiple layers in their cage? How would I build a ramp thing up to it then? Would the ramp need to be a gradual incline? My guinea pigs don't seem that agile so thats why I'm wondering.

Would a chicken wire type thing be good for the top and sides? I think I remember reading somewhere not to use glass...but i don't remember why.

As I think of more questions I'll post them, so be ready lol

Thanks so much!!