All three metal framed sliding glass doors we had in the split level had metal frames that came with them and those attached top wood stud framing. The local business from which I bought them was bought out by a huge local ACE Hardware ... if that helps at all.

What kind of steel are we talking about? Is this inside a masonry wall or are we talking about so sort of commercial construction?

@Windows on Washington Ltd. It is a mod century modern residential house I’m remodeling. To make the 20 foot opening it is requiring 5x7 HSS steel columns and a beam. We were planning to do black fleetwood sliders but thought it would look weird to have black aluminum sliders attaches to drywall that would be white since painting drywall black I think may look weird so I was wondering if the HSS post can have the door directly mounted to it and if the steel is painted or how these situations are handled

@Windows on Washington Ltd does the wood nailer disguise somehow or do you have to cover the steel post and nailed in drywall or something to make it uniform?

They should have metal frames that attach to the wood that was used to frame the rough opening.. Maybe be a couple of pics of your space /

@Patricia Colwell Consulting @Windows on Washington Ltd

So the hot pink is the engineering design of where steel would go, this would give 20 foot opening (removal of center post). He designed HSS steel beams and colums 7x5. I am concerned that the steel will start looking bulky if I continue to add wood, drywall, etc and am trying to make it as thin as possible also as there is a view from the room to the left (not pictures) and the beam will break up the view a bit.

What kind of climate are you in? You can set the door straight to the steel if you like, we just don't much see that here because of our climate. We can't have bridged steel to the outside.

@Windows on Washington Ltd California climate so moderate. I’m just concerned about having bulky posts at the ends, it seems connecting the door directly isn’t the best idea but I don’t want the area to look weird with big posts and then small side light glass

You are going to need to talk to the architect of builder to see what they are allowed to do via code. If they can attach directly, its doable. Just requires pre-drilling or attachment via straps.

@Windows on Washington Ltd

This is not my house but is there a way that the steel post can be behind? If you have a large like 25ft opening of windows but the structure of the roof is supported in the rear is there any issue with sagging or needing a big header for just the doors?

Can it be done, absolutely. You need an architect and an engineer. There isn't much more that a forum can help you with in this case without knowing the house, current structure, climate zone, code, etc.