Thank-you all for your hints and suggestions. I was experimenting with the suggestions and found that if I first spot tinned the walls, lay the corner braces over the spot tin and heat through the braces, the braces were successfully soldered to the walls. For the door trim and tracks, since these parts are so small. I will try either CA or JB weld. I will let you know. Got to get back to assembling the walls together to make the building.
Once again, thanks to all.
Bill