Currently building an addition to the kitchen with a 25 m2 dining area using a steel structure. Just like in your case, there will be a lot of windows and also a balcony terrace on top, so steel is a flexible solution. The walls will be made of light concrete around the windows and panels over the steel. Everything will be plastered in the same style as the rest of the house.
Have only completed the pre-cast slab so far, but it does have square anchor plates (about 25 x 25 cm) embedded in the corners. The standing beams will be welded to these plates.
The construction is seriously delayed right now, but I'll try to upload some pictures during the fall/spring when the steel will hopefully be in place.