Suppose you could have Sub Accounts under the Savings Acct. Move money in and out of the Parent Acct to the Sub Acct as you want to add money to that project.
But I have to say I don't think I'd be going down that path. I'd rather keep my books clean and only have actual transactions and Accts as needed. I'd be doing Forecast Budgets in Excel or some other Budgeting tool that does not affect my books. And that's not to say you can work out some budgets in QBs, but it sounds like you're just hanging on to cash and not actually budgeting a real project.