have the builder dry wall it closed.

unfortunately with new construction you cannot request and structural changes to the plan, anything has to happen after closing.

I don't necessarily want to close it with drywall, it does bring in alot of light.

Just something to prevent falling over

I would want the wall drywalled closed to have more space for furniture placement against the wall in that room. There is plenty of light there with the double window and the light from the adjoining room through the open doorway. As for the "L" opening, look into a sheet of tempered glass to cover it. You'll have to install support on the walls, but it can be very efficient at letting the light through, and if properly installed, even if a child climbed on top of it they wouldn't fall through. It could be done as glass floors are installed.

https://www.houzz.com/photos/vilters-hall-orange-county-phvw-vp~19461133

Add steel or aluminum framed (cheaper) windows to the area to allow light, but close space off. Congratulations on your new home! Good luck with your move!

I would most definitely want that upper one drywalled over into a full wall. The lower one isnt as dangerous as that upper one, but, I would still want it drywalled over just to have the wall for furniture.

thanks everyone for the input.

For the L-shaped opening, I am leaning towards putting a 1-2 ft tempered glass supported by the walls on either side. The cat could still jump and walk on the ledge but not fall over.

For the window, I'll have to consider the drywall vs. the steel framed windows which I actually like alot.

I wasn't initially thinking about closing the wall since I don't have plans for furniture there. By the floor plan it is a "dining" area for a table, but we will likely dedicate it to the kids toys and crafts so that the rest of the area remains relatively organized.

You need to have a conversation with an independent HVAC company to ascertain the possible effect a "solid" closing would have on the whole system.

If those half-wall areas were instead railing + balusters, would you feel the same way about enclosing it? It would look just like the top of the landing with the guardrail (unfinished railing).

We have ledges like that all over the (3.5-storey) house. Some of them are close to windows (which are suspended 30 feet up). Have had six cats in various combinations since living here, and no injuries -- cats are built for height and seem to know their limits. Have also raised a kid from birth to 13 here -- you know if you have a climber, and if you don't, a few warnings will probably do it. I'd hate to feel enclosed with glass and railings in my own house, undoing half of what probably made you like the place. (I do presume that you'll put spindles in the railings, though -- wide openings down at their height are Too Much.)