Here is a tutorial on how to create a basic Quad grid with variation.

modeling workflow is as follow:

1. create Quad grid (I use a user defined feature which is in the Quad template.zip) 

you need to import the file and create a library in order to reuse it

2 create chessboard grid using Odd/Even + Mix

3 create the centers of the chessboard quads

4 create a attractor curve

5 set the attractor curve to the chessboard quads's centers

6 normalize the value of the impacted center translation

7 scale the chessboard quads by the above value

8 if necessary, transpose the quad grid in order to have proper value for the attraction

Template modelization for the Quads user defined feature

I think it is a good exercise to get started with Xgen modeling logic

here is the zip with 3dxml of the final result

here is the zip with 3dxml of the templateLet me know your way!