I bought a bird hide from a company called Treehouses ltd, did not want to put concrete on green site and thought of carrying paving flags across a field ..... spoke to the suppliers who told me to use ecobase plastic base which they stocked. 3m x3m cost about £200. had a look at it and it looked really strong and very simple to fit. I chose a reasonably level site, laid out the membrane material also supplied by them, and then put the interlocking base together with the locking pins, in all it took no more than 10-15mins. carried the pieces to the site and started building the hide on the base.  after  putting the walls up I used the tie down straps to fasten the hide to the base, really easy zip ties.

i cannot say how impressed I have been with this  ecobase  it has been light ,strong, easy and hasnt broken my bank or my back!!!

If anyone else wants to see it then look at ecobase.biz I would definitely use it again.