I was wondering where the keep in Whiterun is located, what is it's name, and when I arrive there where do I have to go to find the seller of the house that is available for purchase in Whiterun ? (The House is Breezehome)
The keep in Whiterun is called Dragonsreach.
From the main gate, follow the path straight ahead. Once you reach the courtyard with the vendor stalls, head up the stairs to your left. From there, continue straight ahead, and up a few more sets of stairs. Welcome to Dragonsreach!
The seller of the house is located inside. His name is Proventus Avenicci, and he can usually be found next to the Jarl, or sitting at the table.