For the working factors i have a made a program of my own in C++ and its kinda tricky for other users.It wouldn't be proper to share that one.For the structural calculations i used FEA in a computer cluster due to its complexity.
I just got done with a massive oilfield conveyor system, on this one there was very little belt pretension. what kind of material are you trying to move? is it bulk material like sand or rocks or is it discrete items like assembly line parts? Is this indoor or out door? mobile or stationary? Is it engine driven? hydraulic? electric? What are you doing with the conveyor? is it moving loads from a low position to a high position? is it moving loads around a factory from one place to another? is this a continual flow process or does it have to start and stop frequently? there's a lot to designing a conveyor system and these are the questions you need to answer first.
In general, Muzammil Patel,designing something is not just modeling something.There is a whole set of steps that are based on engineering principles.You examine first your need and based on that, you proceed with the steps.So if you need to design one start with what you need to design.Then we could help about the steps one by one, but it is needed a lot of work from you ! Are you willing to do that ?