As a general rule, if the owner hired whoever drafted the construction plans, or if whoever drafted the faulty plans is an employee or agent of the owner, it is the owner who will be liable for defective plans.
Ing to Boundy (2012), typically, a written contract will include: Date of agreement. Names of parties to the agreement. Preliminary clauses. Defined terms. Main contract clauses. Schedules/appendices and signature provisions (para. 5).