Need advice on timber size for floating garage shelving

[jaronemo]

Looking to make 600mm deep shelves with a pine box frame with mdf board sitting on top, with either metal or pine supports. Will span 3.5m along biggest wall and 2m on other 2 walls making a U-shape at one end of the garage. Biggest wall is plasterboard and the internal frame uprights seem to be about 450mm apart. Will be single shelf sitting about 2m off the ground, 800mm from the roof.

My question is what size and type of pine shall I use for the frame? Have seen both framing pine and dressed pine used before. Aesthetics isn't a concern.

Apologies if this makes no sense. Can't upload photos from laptop.

[Jason]

Great result @jaronemo, congrats. Many thanks for coming back and sharing the photos. 

Jason

[Poppop]

Looks good @jaronemo. It's a good feeling to look back at a successful job knowing the labour costs are still in your pocket, isn't it?