How do you make a sofa that converts into a bed?

Simply put you make a box and give it a lid that telescopes to double its size.

OK! But how do you do that?

Well since a picture is worth a thousand words, here's 3000.

This is one half of the lid. It is in two halves to reduce the weight that will have to be lifted when accessing the storeage underneath.

The reason for the gap in the middle is that I've used up my supply of timber so I shopping trip is needed to finish this and to make its twin.

When completed the bed will be 2m x 1.4m, big enough even for me!