Hello,

I am needing to construct a door frame for a 7'x7' garage door. Any
pointers on how to make the strongest best frame possible?

The timber merchant advised me to use 3"x3" wood and to treat it
myself. He said anything bigger would be too big and heavy. Do you
agree?

Is any treatment better than any other?

Another merchant said not to take the frame to ground level so it does
not get damp, but I'm not sure that I can do this; after all, if I
leave a gap, doesn't that give thieves a point to insert a crow bar?

How do I make a suitable mortise? is it time to buy a router? How deep
should the mortise be?

What frame fixings shall I use: are some more secure than others?

Thank you very much.