This is a new construction house.

I have a cathedral ceiling with a 4" x 16" structural beam that needs to be covered. This is a country style house with the ceiling to be covered with 1x6 t&g white aspen boards. I want it to have a look of a rough-hewn solid wooden beam. I likely will have to widen it with 2x4 runners also so my electrical works out. Where can I buy the wood to cover it to give it the look I want. Any other suggestions to cover this beam would be appreciated. Thanks.