How to build a platform deck ?

I want it aprox. 12X12 and in (4) sections in order to move it as needed to other areas of my yard. I don't want to use treated lumber if it's a lot more money. I'm thinking I have enough 2X4's for framing. I plan on placing the deck on cement blocks to keep framing off the ground. What board widths do you suggest and how many do I purchase? I think Lowe's will cut them to size for me. Thank you for any real advice you can offer. Please...no smart aleck responses.