So a few days ago I decided to research and build a cardinal house. Cardinals do not like your normal (cavity) bird houses. They are what is called platform nesters and will normally nest in tree branches.
I used some poplar wood and poplar dowl rods to build the platform below. I put a few twigs and dried grass to hopefully attract a pair of cardinals. If not this season maybe next.
I am using paracord to secure the platofrm to the tree and the open face is towards a suet feeding cage that I just installed at the same time (see below).
Someone may be interested!