All of our gazebos are sturdy enough that they can simply be placed on your lawn without the need for a special foundation.  Your site should be level and compacted.  It is also a very good idea to put down some type of weed barrier to prevent the grass from growing up in the tiny gaps between the floorboards.  Another option is to place your gazebo on a concrete slab.  This is the ideal situation as it gives you the most solid foundation on which to set your gazebo.  A compacted gravel base also works well.  In the event that your site has too much slope for either of the above foundations, or you would like your gazebo elevated, you can install your gazebo on posts.  This also works good when you want your gazebo incorporated into a deck.