For Falkreath: You must complete the “Rare Gifts” favor, and the “Kill the Bandit Leader” favor. You may then buy land from Steward Nenya.

I did what it told me to do and still have not gt the option to buy land.

Try that:

• Side with the Stormcloaks so Dengeir replaces Siddgeir as Jarl.
• Talk with Jarl Dengeir (he will ask you to become Thane again)
• Talk with Tekla, the newly appointed steward, and she will give you the option to buy land

Also, you could have a miscellaneous quest in Falkreath that needs to be completed. It doesn't matter if you're Thane, just having that quest active could lock out the conversation option.

After killing the bandit leader, did you return to Siddgeir? You can't go straight from the bandit lair to Nenya. Once you tell Siddy that the bandit's dead, then he'll let you buy the land from her.

Thanks for the tips Mark41 and Ghastley I will see if this helps.