What sort of card do I need?

[babybouncer]

Hello!
I have decided to make a sort of suitcase pop-up dolls house for my daughter and I now realise I have no idea how to! I have a small child's suitcase and my idea is to buy a few bits of wooden furniture to keep in the case, construct a floor over the storage area and some sort of walls. I can work out how to create the storage area, but I'm not sure what to create the floor from - needs to be sturdy but not too heavy - and I have no idea how to create 'pop-up' walls for the back and sides. Any ideas of what sort of material to use? How can I make it hinge and how can I make it stand up?
Any ideas gratefully received...

Would grey board work? It's fairly easy to cut and is reasonably sturdy.

Not sure about hinges and standing up - maybe masking tape hinges? For the standing up bit could you cut wedges out of the bits that will stick together, to act like a joint? I don't know how to explain that any better - I'm thinking woodworking joints.

Will you be decorating the walls and flooring? How will the flooring be pulled up to uncover the storage?

Ah, here's what I had in mind.

Thanks Hexie - I like that idea. Where would I get grey board from?

I got some from Great Art a while ago. If you have a Hobbycraft near you they should have it, or an art or office supplies shop would be worth a try. I suppose mounting board will be similar but may be more expensive.