Architecture Real-time ( my first project )

UE4 is free*

There is a 5% royality for revenue over $3,000 a quater, but that does not apply to certain types of arch-vis work, including

Consulting fees or work-for-hire fees which are non-recoupable for services performed using the Licensed Technology (e.g., an architect-created walkthrough simulation or a contractor-developed in-house training simulator);

Revenue from a Product which solely relies on the Licensed Technology for production of non-interactive linear media (.e.g., broadcast or streamed video files, cartoons, or movies) and which is Distributed in a form that does not contain the Licensed Technology or, in order to deliver, rely on servers running the Licensed Technology;

Read more here: EULA - Unreal Engine