To fold your own receiver you will need a press, most start with one like this.
Then you will need a flat bending die like this, some builders make their own.
I see your barrel has not been removed that will take a Barrel Pin Tool like this to press it out.
Good luck because some of them can be a real pain to get out.
Next tool needed would be a trunnion drilling fixture, if you have a drill press you could try just lining up the rivet holes & doing it with out one but the rivet holes turn out better with the fixture. Here is two to choose from.
The next tool needed will be a spot welder to weld the lower rails in, it will also need a special lower tong, some builders rework the old tong & get it to work.
After the rails are welded in you will start riveting & will need a trigger guard rivet jig.
At this point your are most likely thinking it would be easier for me to buy a receiver. Yes it would be easier to buy a receiver but you won't get away that easy, even a bought receiver will need to be riveted. Then you will need a riveting tool like one of these.
This one will do all the rivets except the trigger guard rivets.
or the long rivet jig & short rivet jig here.
If you encounter any problems there will be extra steps and/or tools that are needed to complete your gun.
There are short cuts to doing a lot of this building and a lot of jig & fixtures that you could build your self, if you have the time and patience to do it yourself.
Good Luck with your build!