(New structure) Forest sanctuary

The Forest Sanctuary is an small structure that could be generated only in forest biome. That structure works like an inverse of witch's hut: instead spawning mobs, it won't allow an hostile or neutral mob spawning in the area, only an passive mob.

It should be made by an combination of fences, slabs and planks of oak and birch.

The Sanctuary could have the size of 8x8 blocks in the base, and 4 or 5 blocks tall.