To transfer money from one fund to another fund, create a new transaction.
Type "transfer to building fund" or something similar in the description field.
Then select "Deposit/Credit" from the transaction type field. Select the fund you want to transfer the money FROM and enter the amount of money to be transferred as a negative amount (-1000.00).
Then click to add another entry. On this second line, select the fund you want the money to go TO, and enter the positive amount (1000.00). The Transaction Total should equal zero because you are subtracting from one fund the same amount that you are adding to the other fund.This will not affect the balances in your accounts, as no money is being withdrawn or deposited in the actual bank account. This is simply reallocating money internally between your fund "buckets".