If covering entire surface, need to make sure that have proper drainage. If building from scratch, could do tongue & grove for solid deck as long as have gradual slope outward for water to move away from house. This slope is not necessary for deck with board spacing. Not sure how carpet would affect this. If not concerned about view from below deck, could you attach a large screen under entire deck? This would be cheap, not very visible from above and have no effect on drainage.