There are several ways of making books. Sheets of sugar or craft paper stapled together with a cover of vinyl wallpaper is the quickest and simplest method. Good quality board or card joined with heavy quality passe-partout is stronger still. For small books postcards (used double by sticking them together with Sellotape) are easily available and work out cheaper than a good cardboard. books made in the usual way with leaves folding back from the spine need strengthening with a suitable adhesive tape down the spine.
The difficult part is finding the picture material. Some talented people are able to produce this for themselves but most of us have to rely on collecting from every possible source until we have enough to complete the project. Since it is important to follow a theme and use pictures which are consistent in style this can take a long time. The most successful home-made books often result from using good picture material linked by simple felt-pen additions. Making books is not a cheap under-taking if it is done really well. The advantage is in being able to produce something which the children need or which encourages a particular interest which cannot readily be bought.