I don't use allegro however can answer some of your queries.
I want already created ball grid array components
Do you know how many BGA packages there are in existence? And you want someone to provide you with them all?
I suggest you hit F1 and read the help file on how to make components, a BGA is easy to make in comparison to a connector because it is usually just the same pad size repeated.
i want know to set origin and also center of body components
As above, the help file will tell you this - look under how to make components.
Did you search on search engines for this? a simple search brings up
this link on this site that explains how to change the origin so would give you some information on where to look.
Or even
this pdf file thats explains some towards making components.
how import to PCB layout and Gerber file.....
Now I know that you have not searched - either Google or on this very forum.
https://www.edaboard.com/threads/200794/
You may think I am being obstructive - I am not.
By learning how to use the CAD package that you have chosen to use you will be able to make your own symbols, components and parts.
by reading the help files, the tutorials and associated documents you will learn more about it and improve how you use it.
By searching the internet or forums like this before you ask a basic question about something that could have been answered by you learning to use your CAD package you:
A - find the information you seek a lot quicker - someone else has always asked it before you.
B - will obtain your answer a lot quicker
C - do not look like someone who is lazy and not prepared to learn their own package nor search for their answers - they wont all come on a plate.
Have a nice weekend.