Devils in the Details

You create a contract (in your favor; of course,  that must be approved by the DM).  Two creatures that sign the contract (including yourself) are beholden to the terms of the contract until the contract is destroyed (by a disintegration ray for instance) or successfully dispelled.  A time period for completion will always be included in the contract. 

If the contract isn't completed by that time, the offending party will take 5d10  psychic damage each day until the contract is satisfied.  Any hit points lost in this manner are deducted from that creature's hit point maximum.  If a creature's hit point maximum is reduced to 0, it immediately falls dead and becomes a monodrone under the sway of Primus on the plane of Mechanus. 

The contract can not be written in such a way as to cause either party to be forced to take an action that would cause them harm or death.

Prior to signing the contract, any creature can make an intelligence save against your spell save DC to determine that the contract is magically binding.

Either party can end the spell early by visiting the plane of Mechanus and convincing Primus to decree the contract Null and Void .  A wish spell also ends it.

You can only have one contract active at a time.

At Higher Levels. When you cast this spell using a spell slot of 8th or 9th level, for each level casted above 7th Level allows for another creature to be bound by the contract.