Doing something that big for the first time can be like high-stakes gambling. It could go either way. But even if you feel you can gt the job done and you plan on not amking a dime, like the other psots said, if the client doesn't have the money don't even waste your time making a viable quote. If you want do the homework and general costs down on paper, and all your ducks in a row---for next time. I dug a 300,000 gallon (approx.) pond that was suppose to have a 70' x5' wide winding waterfall and secondary reflecting pond. I had a lot of great ideas and the owner loved them. Got the pond dug, the waterfall lined and most of the rocks in. Then reality struck and he had no money left to finish it. That was three years ago. Now there are 4 foot weeds growing around it and I see it every day. It looks bad on me but I'm not about to spend any more money time or resources on it. Plus he took 6 months to start paying a little here, a little there. Just today he said he wants to have me enlarge the pond. Great! More work I won't get paid for.