Make sofabed fromm pallets

Hi ,I am making a sofa bed from pallets,
I need help in understanding how to make the extendable part.
The back support is fixed and does not move
The extendable part is from the bottom.
I want to be able to raise it to the seating portion and when not in use want it to be folded and stored under the seating
Questions
What should i use to fold the part?
I am adding wheels for easy pulling ,how will I raise it to the level of the seating?

Thanks