My problem seems to be very simple, but the simple things sometimes are the most difficult ones

I hope anybody can help me solving the following problem:

I want to model sails, both for boats and for shading purposes. They should have the forms of triangle, square, pentagon and hexagon and can be flat (like a plane). Each edge tends to move to the direction of the center when it is under suspension. If the edge-length is 10 meters for example, the middle of the edge goes approximatly 30 cm to the center. Look here: http://img99.imageshack.us/img99/9720/segelproblemoo5.jpg

Until here it is quite easy. Iâ€™ve done it using PET.

But I want to resize the sails in a fast and intuitive way, and the relations between edge-length and suspension distance should stay the same. For example: I would like (to show to customers) to put one corner of the triangle (square, â€¦) to the corner of a house, but I donâ€™t want to model the exact form every time newly.

Do I need a Python script to achieve a solution?

Thanks for everybodyâ€™s help!!

Karl