What would be your collection of reptiles? Would this be just your reptile house in your zoo or would you make a zoo specializing in reptiles? About quantity, 30 species is a good number, but if you want, you can put more or less; It depends on you (preferably, try not to exaggerate). If you want, you also can describe the location of the enclosures, their size, their appearance, the amount of animals of each species, draw a plan... If you want, you also can include other animals like amphibians, fishes and invertebrates.