I need to have my X/Y axis align to a wall instead of the grid

I am working on a structure that has walls running at 45 degrees to the standard grid, and it would make things a lot better for moving/aligning/etc if I could temporarily have the X/Y axis align along that wall and not the regular grid.

I’ve done a number of searches and looked through various tutorials and have yet to find a way to facilitate that, so I could use some help.