I built a shoe cubby around my hall radiator. I cut slits in the sides of each shoe cubby so we have warm shoes in the

That's really cute!!

Roarah has beat me to the suggestion and that one looks very nice. My suggestion woud be vary the radiator cover design for better air movement. Although the name is radiator, most of the heat transfer is by convection.  You want a design which will create air movement as the warm air rises and cool air is pulled in at the bottom. The warm air needs a clear path so allow an open area above the radiator, perhaps as high as the distance from the wall to the front of the enclosure. Then a solid panel across the front. Inside the cover use a piece of metal or other material to direct the air to the front and not get caught in the dead space under the top against the wall. I used a piece of marble from ReStore for the top in my foyer but any remnant of solid material woud make a durable surface. 

If you wish to research further, search for info at the heatinghelp web site. There is tons of useful info at that site.

I used the measurement suggestions from the below link and used metal as heat reflectors in all my rad covers. https://www.homeserve.com/uk/living/home-and-lifestyle/do-radiator-covers-block-heat/

My current house is forced air heating and I really miss the radiators! I do enjoy having central air here but there's no substitute to sitting on a warm radiator cover after coming in from the deep freeze.