10x6 shed wall timber frame size

Hello, I am looking to build a 10x6 shed for the garden tools etc. Pitched roof. 1 door. 1 window. Unclear if 2x2, 3x2 or 4x2 should be used for the wall frames. Sure, the "bigger the better" makes it stronger and potentially more durable. But I intend to keep the costs to what I need, so was considering 2x2 PT. One thing I am unclear about, which none of the youtubes or web sites seem to have covered, although many do say 2x2 is OK to use for the wall frames, is how you butt join 2x2s at 90 degrees, i.e. the frame. 2x 5x90 screws into the end of a 2x2 doesn't feel right. Expert guidance is always welcome. Thanks, in advance.

Hi I am about to build a similar size shed as yours, you can forget about using 2x2s, think you should use 4x2 for main wall frames. Why not have flat roof its only a small shed. I am also considering plastic sheds at moment but not sure how solid they are long term.

Use 3x2 CLS above ground perfectly strong enough for a shed the size that you are making, I've made a summerhouse and in process of finishing a shed build with the above timber, 4x2 for raised floor frame and roof for my 12x9 shed, pics attached.

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Thanks JayDIY and pach1962. I didn't need much convincing to change the 2x2 idea. I just wanted to hear it from real people iso people trying to sell me something. Stay safe.