Assalāmu `alaikum Warahmatullāhi Wabarakatuh. 
Q: Mr A wants to buy a property for £150k, he doesn’t have the money, He ask for Qarz e Hasanah from Mr Z.
Mr Z proposes, that Mr Z buys the property for £150k and Mr A can rent it of him at a fix rent, Until Mr A has the money to buy it back at £150k, within 1 year, if Mr A doesn’t have the money at the end of the year then Mr Z can sell the property for any amount and keep the money, e.g: if he sells for £160k he keeps the £150k plus £10k = £160k
Mr A can ask for extension period at the end of the year, at the discretion of Mr Z.
Is this permissible?
Jazakumullah Khai raa ( may Allah reward you with good ) 

– – — —- —- —- —-  —–  —— —–
Wassalāmu `alaikum Warahmatullāhi Wabarakatuh.                        
Answer
It’s is permissible, the loan agreement should be made for a fixed term after the property has been acquired