Francisco Guinea - IMDEA Narrow electronic bands arise in different arrangements of graphene layers. The effect of the long range electron-electron interactions is analyzed and compared for small angle twisted bilayers, bilayers and trilayers in a commensurate arrangement with the BN substrate, and twisted pairs of graphene bilayers. It is shown that changes in the electron density alter in different ways the electronic structure. A classification is made into systems where the shape and width of the electronic bands is highly sensible to the amount of doping, and those where the flat bands shift rigidly with the number of carriers.