Does anyone know at what time we should pick them to make perry or do we just let them drop. Also how do we make good perry?

I would say autumn time when they are ripe, you can tell if you cut one open, see if the pips are dark brown or almost black, if they are white they are not ripe. it is also best to pick pears not to let them drop because they will get bruised.
Sorry don't have a clue how to make perry.

You still have quite a while to wait for your pears to ripen. Normally round about September or later, depending on your variety. But, in the meantime check this link about perry, and for the instructions of making perry at home.

http://homepage.ntlworld.com/scrumpy/cider/perry.htm