Learn Hardcore Croatian: Naručitelj radova plaća u mjeri u kojoj su radovi završeni. - The client pays in proportion to how much of the work has been completed.

Naručitelj is a formal/legal word meaning the party who orders or commissions something. In a construction context, it often means the client, the employer, or the commissioning party. It is not the worker doing the job, but the person or entity for whom the work is being done.

Why is it naručitelj radova? Why is radova in that form?

Radova is the genitive plural of radovi. Here it works like English of the works.

So:

naručitelj = commissioner / ordering party
radova = of the works

Together, naručitelj radova means the commissioner/client of the works.

This is a very common Croatian pattern: one noun followed by another noun in the genitive to show a relationship.

Why is plaća in the present tense?

In Croatian, the present tense is often used to state a general rule, especially in contracts, laws, instructions, and formal statements.

So plaća here does not necessarily mean is paying right now. It means something more like:

pays
is to pay
shall pay

In legal or contractual language, this is very normal.