Fred wrote:
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.

A screwed half lap joint would be easier, and only needs a handsaw. If
this is an up and over door, there are probably plenty of places to
insert a crowbar. Alternatively, whack a load of grease on the end where
it meets the ground.
Best to make a 4 sided structure and brace the corners. Something this
size will creep out of square if you don't make it rigid. The bottom bit
can be a piece of scrap but it keeps everything square while you fix it.