With the building savings contract, you have the disadvantage besides the closing costs that you do not receive any interest on your savings rate. Additionally, with an 80`€ building savings contract, you still need an additional loan of 60´€, which is expensive due to the small amount and, because of the land register priority, can only come from the same group as the building savings contract. You only get the low building loan interest rates with very fast repayment. Therefore, in my opinion, put all other money in einen World or allworld ETF and be done with it, and reconsider it no earlier than in 5 years.