General dimensions for a uav type rc plane?
You can start by looking at plans here to get a general idea. When it comes to planes you can't just get some "general" measurements and wing it (pun intended). There are a lot of considerations when it comes to making things fly. With out going into specifics it would be best to use known working plans to build something as apposed to trying to throw something together that looks right. 

To Answer your question directly that picture looks like the wing span is the the 3.5 foot range, the center section is about 2.5 feet long and tail poles are about 18 inches.