What I did
- The skooma questline.
- 5 Misc quest from riften citizens.
- Collected the 8000 Gold.
After that, the Jarl told me that I can buy a house from the steward.
If I talk to the steward I have the option to buy the house but if I click it, the only option I have is saying "I'd rather wait some time and think about this decision again". I already tried waiting a long time. But that didn't help.
I'm level 13, if that matters.
Best Answer
This is known glitch. Here's the only info about a bug related on the wiki:
One solution is to help more people in Riften, like giving donations to beggers, giving a healing potion to an argonian worker, helping Brand Shei for evidence about him, giving materials to Madesi, bringing Fire Salts to the blacksmith.