A piece of wood 2x4x6" dropped on top of my husband's head from the roof of the storage. he felt mild headache and pain the first 2 days, it's getting better. there is none of any other symptoms so far. does he still need a check up like x-ray etc.?

If he experienced a minor closed head injury and is now improving, do not see any need for medical attention. If he gets worse, then get proactive.

There is a questions of whether or not if he had a mild concussion. If there is not break in the skin or an indentation then x-ray is not necessary. To be on the safe side just observe for any mental changes, return of the headache, nausea 4 weeks from the time of the initial injury. If these symptoms occur then present to ER immediately. These are normal head injury instructions.