Dave has a home office in his garage and he wants to get Wi-Fi out there, rather than having the wired connection. Leo says that he should be able to get Wi-Fi for at least 150 feet. If he has a lot of wiring in the walls, then he could end up with slower Wi-Fi, or even a dropped signal. The easiest thing to do is to find a repeater that's the same brand as his Wi-Fi router. They're essentially routers that are in "bridge" mode.
He should put that somewhere in the middle, and it'll just pass the signal along. He can add more than one if he needs it. Line of sight would be a good idea as well. Another option could be powerline networking.
This would use his power lines as an ethernet bridge to extend his network without additional wires. It's gotten a lot better in the last few years.