Contest 11

Inspired by our presentation on pentominoes, during the Nationale Wiskunde Dagen in Noordwijkerhout,some of the teachers at the 'CSG Liudger' in Drachten-Friesland-the Netherlands, made a booklet with questions and problems about pentominoes.
We got our competition from that booklet

Here , you can download this booklet.
It's in pdf-format, you must read it with

Construct a bridge where every step has size 1, 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 108.
Try to maximize the enclosed area.

Use this to help the search:

'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 .