Update:

To avoid some of the issues that come with attaching touch sensors to cardboard boxes we have changed the platforms slightly. They will now we made of corrugated plastic which should be a stronger material. The platform is supported by four trusses on the corners and a metal frame underneath it. It is still the same height and dimensions. If you are concerned about weight when your drone lands we can assure you it is sturdy; we dropped a 25 lb. bag on it and it held fine! Image below.