1. You can use almost anything from rubble; roof tiles, slates, bricks. I was lucky to find a curved one.
2. Simply get a good 'design' with a doorway at the front but covered at the back
3. Place somewhere damp, near a pond is good, or where there is anything decaying, Frogs and Toads love that!
4. Nicely hidden, mine is buried among the One Day Lily's and other plants.