"Has anyone built a room to close up the two story? I would love to do that."

I know someone who just did that...not because of noise..to create an additional bedroom... I haven't seen it yet...but apparently it can be done...IMO, as they did, you would probably need an architect to come up with the plan in order that the support be sufficient.

I'd suggest that you do NOT want to build rooms here without an architect involved. But even there you might consider what it would do to the resale value of the house. Especially since you love the way it looks as is.

Why not deal with the real problem? If there is noise, then solve that problem instead. Add more noise absorbing materials in the room. If the floor is wood, then add area carpets, maybe oriental rugs. Get some wall hangings. I'm quite confident that there are experts in noise abatement to be found. Find a contractor who deals with these problems. For example, there are sound deadening materials that might be applied/attached to the ceiling. This will cut the sound without hurting anything. If you cannot find a contractor, the internet is a great place to start. Check out the link I've attached as a start.

And, these ideas will be HUGELY less expensive than the large cost of building renovations that you will one day regret when you try to sell a house that nobody wants. Worse, structural problems that come from a poorly implemented renovation in a structure that was never designed for the extra loads in strange places. (This happens even in new construction. An engineer friend once figured out that the way their house had been built, even a moderate snow load on the roof would be enough to collapse the roof. They got it fixed.)

John

Here is a link that might be useful: Noise abatement

If the noise is concerning in the two bedrooms upstairs, then you might the following:

solid core doors
adding a french door to the entry to the bedroom area. Our home has a two story great room and three bedrooms upstairs off a small hallway/catwalk. The addition of a simply french door is attractive and can be closed to limit noise from carrying
The addition of carpets and other materials to soften noise. We avoided hardwood in the great room for this reason.

Hope this helps!

cork flooring would help deaden the sound.