sugam:
I understand that runways at commercial airports are atleast 6000 - 8000 feet long and am trying to figure out the length of an ideal runway for business jets.
As the other two knowledgeable gentleman have said runway length is just one of many, many factors. If you were building an air park for light airplanes, it can be an easy undertaking. But, not so with business aviation jets. In that case it is somewhat like building a small airline airport. In addition to length and width there are load bearing issues, clearway issues, etc. And, there is the issue of having instrument approach and departure capability, which requires an airspace and obstacle assessment and related surveys.
As to the first basic question you ask, I can say that a runway of 6,000' length with a 75' width (100' preferable) is adequate for long-range biz jet operations. But, again, 7,000' would be preferable.
Bottom line: you need the planning and work done by experts who actually build runways/airports.