I have done everything for the Jarl and his steward, and I still don't get the option to buy a plot of land.

Anyone know what I may be doing wrong or missing? Anyone else having this problem?

Thanks in advance

Markarth has a house, Vlindrell Hall - it doesn't have a plot of land.

There's a couple of bugs that may prevent the option of buying the house from showing.

If you're on PC there are some console commands that may help. I can't post links so you could search for can't buy Vlindrel Hall or similar.

Perhaps he meant Morthal? In which case it is a ghost and a ruined house to investigate, you need to ask around Morthal for clues.

If not you are going to have to be a bit more specific, you posted in the Hearthfire section so presumably it is related to Hearthfire somehow.