Before you start building on top of the deck. You should let it sit and breathe. It may settle in one or 2 corners and trying to fix it after you put more dead weight on top of it will be extremely difficult. Try to get everything square and level before sheathing. For squaring you can use the 3,4, 5 rule. Which is a triangle. Pick one corner measure 3' one way 4 ' another and the hypotenuse should be 5' if not than you will need to adjust.
You will also need some basic carpentry tools such as a tape measure, square, level , saw, hammer and a shovel. Don't forget a few safety items such as eye protection, ear pro, hard hat and steel toe boots. And by the way you don't need 8 men which are way to comfortable with each other to build it.