Not real sure how you write a complete weld procedure for this joint: The sides are really just two simple thin piece of carbon steel, the inside is a tight 90 degree fillet, the outside corner is two flat pieces touching each other with a very, very thin sliver of steel at the extreme corner.
1x1x1/8 thick sq tubing is very thick, but you really don't have much metal there for any kind of "weld prep."
If you have 14 gage steel walls like I use for railing and frames, you can't really make any prep at all. Just fuse the two touching steel, working very hard not to burn through the wall. 1/8 will be a bit easier to work with, but I'd worry much, much more about burning through and having to frequently "fill in" the hole rather than worry about the prep.
A conventional 1/8 steel prep on the sides will have a 1/16 flat, then a 1/16 "bevel" - very difficult to machine accurately. (The 45 degree cut of both tubes is more important for your fitup!) Your first pass will completely fill the joint. Assume a weld heat or feed rate of 2 is used.
On the inside corner, your welders will have a fillet joint that will tend to either burn through or not get good fusion into both tubes. Access won't be easy. If they use a MIG welding process, they will have to swing the nozzle across the joint to get the base metal in both tubes melted. on this corner, maybe a slightly slower speed, but a slightly higher wire feed rate or slightly higher heat input.
On the outside, you will melt and round off the very skinny corner. Here they will need to reduce heat, reduce feed rate of the wire, and work very hard not to make holes.
Remember, the purpose of the bevel in the weld prep is to ensure your welders can reach the inside of the weld on the first pass. If you have a process spec for welding thin carbon steel, you don't need another. Just practice and isstruction.
