It doesn't sound like you're ready to buy. Unless the seller is motivated to wait (ie: hasn't found a new house to move into yet), I doubt you'll get a 4 month accommodation. And if you're saying the house is empty, my guess is they want to sell ASAP.

If you don't have the money now, do you really think 3 or 4 months will make that much of a difference? In the meantime, the market could change in any direction - mortgage rates could go up or housing prices could go up - putting you in a worse position than you initially started in.