What are these different type of tiles used for?

eave tiles would be used to start the roof generally a shorter version of the roof tile goes under the first slate , tile and a half's at the ends to allow for the set up of the roof allows for correct overlap of the tiles gives a bigger area of slate to be secured at the verges less chance of being blown of by the wind less chance of leakage at the verges slates should be nailed twice to secure properly, roof tile is to cover the main roof area slate roof should always be double slated at the top and bottom of the roof if done correctly, good luck Alex.