I'm going to build my first Wifi controlled car. I'm looking for a good ready to use chassis, so I don't have to spend time to build my own chassis and install in it the motors.
More or less I'd need a chassis pretty large, 500mmx300mmx150mm.
Do you maybe can suggest me a good ready to use chassis? or a good way to build it on my own?
For something that big there are pre-built chassises with motors and gearboxes available. However, in that size range better quaility than what most people could build by themselves doesn't come cheap. For example, the six wheeled version of the Wild Thumper (http://www.pololu.com/catalog/category/88) is only a little smaller than the dimensions you gave and can cost around $250. Although I haven't gotten my hands on one yet, more than a few people on the forums have successfully used them on fairly rugged outdoor terrain.
I guess you have to decide how much your time is worth to you...
I also found this similar platform:
I guess that if I build it on my own I better know my robot, but if it's possible a good redy to use platform it's better.