Giant Book set design

 As suggested broadway [soft] flats are the way to go & skinned on both sides, using unbleached calico rather than canvas, as it's cheaper & lighter.

http://theatre.sjsu.edu/~culley/PartsFlat.html Or just use 2 flats back to back, which may be easier & more stable.

If you have a flush smooth stage deck rather than use castors, because of the 4m wide you could use strips of old pyle carpet, fixed to the underside of the flats bottom rail with the carpet pyle face down onto the deck. You will find this is a more stable method of paging the flats.

Also utalise a 'ledger' timber on the flats, as suggested by Logos,especialy if each page is made up of more than one flat, also use a 'dutchman' masking to cover the flats jionts & in view edges of the page flats. This can be strips of calico painted on with the base colour paint, rather than masking sticky tape which will crinckle with any movement. 
You could think about using  Cortec Scenery which may help with you being a school, cardboard could be a good option for skinning the booked pages.