At 5MHz you have a wavelength of approximately 60m. So for a dipole antenna (the most basic) you'd need approximately 30m of wire.

You'd have a length of coax cable going to the centre point of the antenna, so pair of 15m wires extending from each side.

Getting your amateur radio license covers this in more detail.

Dave Casler has a bunch of useful videos on things like this: https://www.youtube.com/watch?v=18-6sJHk9hU