On Sunday we noticed a pair of Black-capped Chickadees (Poecile atricapillus) intently checking out the nesting box located in a tree outside our kitchen window. One bird would enter the box, stay for a minute or so, and then exit the box. At this point the other bird of the pair would enter the box and repeat the process. They went t this for quite some time. We think they must have found the accommodations to their liking; Shara and I both saw Chickadees entering and exiting the box again on Monday.
It's not to late to put out a nesting box. The cold, wet weather seems to have delayed nesting for many species. I use the plan below for all of my small nesting boxes - I am not sure of the original source of the plan as it is found all over the internet. They are very easy to construct and can be built in less than an hour even by someone with no woodworking experience.
One note on construction: The box outside our window was built specifically for Chickadees so the entrance hole is only 1 1/8 inch diameter. We live in town and there are lots of House Sparrows - they would quickly take over the box if it had a 1 1/2 hole as shown in the plan below.