hi oogalepbo, welcome to the forums
there is a basic marine starter guide at the top of the page
viewtopic.php?f=5&t=23675
this will give you an idea of where to start
i made the mesh top by sandwiching mesh between 2 layers of MDF
both with a window cut out, top layer extends over the gap
bottom layer fits inside the gap and screwed together
then polyurethaned or painted to make waterproof