I have a Scotts built by John Deere, riding mower with a 17 hp briggs and straton engine. When I start the blades the engine blows a lot of smoke. When I check the oil level before starting the engine It is always low on oil. I do not see an obvious oil leak so I don't know what is happening. The engine also runs rough. Can anyone tell me what is wrong?

It sounds like it has bad piston rings. I could be wrong since I'm not entirely familiar with this lawn mower, however, when you get oil smoke on a car, it's usually bad rings.