Building contracts are, in principle, no different from any other contract for goods or services. There is no need for the contract to be in a particular form, or in writing. A verbal agreement formed by a householder with a passing tradesperson to repair a chimney stack is perfectly legal. The householder is inviting the person by simply having the stack there, the tradesperson makes an offer to do the work at a price and the householder accepts. The essentials of a binding contract are, therefore: