D&Dtools1

You cause a block of stone to turn invisible and hover at a designated point in the air.
The stone remains there until triggered, either by special conditions set by you or by a command word you choose.
Once triggered, the stone trap turns visible and falls naturally.
The stone of the stone trap can be positioned so that it holds up additional material within the weight limit of the spell.
For example, a 2,200-pound stone with stone trap cast on it by a 13th-level cleric could support an additional 400 pounds.
This additional weight could be placed on top of the stone in midair, the stone could function as a plug in a hole in a ceiling, and so on.
As a trap, the suspended stone has an attack bonus equal to your caster level.
Any creatures hit by the stone when it falls take 1d6 points of damage for every 200 pounds of weight, plus 1d6 points of damage for every 10 feet the stone falls, for a maximum of 20d6 points of damage.
Anything atop the stone might deal additional damage, but such supplementary material can only deal damage above and beyond the maximum (20d6) if it doesn't rely on the fall to deal that damage.
The conditions for triggering a stone trap can be as simple or as elaborate as you desire.
Special conditions can be based on a creature's name, identity, or alignment, but otherwise must be based on observable actions or qualities.
Other intangibles such as level, class, Hit Dice, and hit points don't qualify.
For example, a stone trap can be set to activate when a lawful evil creature approaches, but not when a blackguard approaches.
Arcane Material Component: A drop of blood and a pebble.