Challenge 7

Construct a flight of steps, where every step has size 2, and a landing of any size, with one set of pentominoes.
The pentominoes must touch along the full edge of the square and not just at the corners.
The area enclosed by the stairway must be one part.
Our example shows an enclosed area of size 140.
Try to maximize the enclosed area.

'FlatPoly2', a programm by Aad van de Wetering, can be of great assistance when trying to find a solution. It can be downloaded at his site .