Type of ceiling

The kind of ceiling that I had was the old 2' or so tounge and groove and then it had the 1ftx1ft square white press board panels nailed to that. I was going to replace with 1/2 ' 4x8 sheets of OSB but I was told that there was some type of 4x8 sheets of some type that was already white and was cheeper than OSB. My porch is about 6x 16, and the height is about 7 foot so I do have clearence

It is my understanding, OSB is the least expensive that would do the proper job....around $6 a sheet