I don't know about 40 acres worth of tarp or plastic. Before you did anything you should contact soil people to take soil samples to make sure that your land could even hold water good enough for a lake. Then you'd have to see about underground cables, pipes, etc. Once you got that cleared you could. The first thing you need to make though is a boat ramp. Got to be able to get out of the lake that you create. Make sure you have a shallow end that you can get the digging machinery in and out, and make a levee that is strong enough to hold the water pressure. Depending on depth and location it could take anywhere from half a year to 5 years for it to fill up fully. If you have the land and resources, I'd say go for it. It's something I've always wanted to do. It's your oppertunity to design your own fishing paradise.