You might want to say that a big movie can be defined as that project which is made with the highest of budget and exotic locations. But that is not the real essence. A big film means it must have big names associated with it and this is more mandatory if the film is made on period backdrop.
Any movie which is about warriors, kings, queens should have branded stars. Only then it gets a big color and aura and that attraction quotient. That is how the collections will also work at the box office. Tollywood can boast of three big examples in this aspect. Interestingly, these three movies came in very recent times.
The magnum opus Baahubali became a unanimous winner not just in Tollywood but throughout India. Then came the historical Rudramadevi and despite all the flak, it got break even and landed in safe zone. The third is Kanche and though it got divide talk it still managed to overcome that and emerge as a winner. The major reason for that is the star power.