WOW, that's a great space to work with.

Where is the water and drainage source? What is the view from the wall of windows?

Are you thinking of walling it off or are you able to keep the whole space open?

Hooing for suggestione!

Where is your architect/designer/builder in this?

For help here, post a dimensioned, to scale floor plan.

Detail all the roof heights and slopes.

Say how big the bedroom and bath needs to be, and if you have a preference as to their locations.

Should have stick framed it. Then you could have had dormers, and actual head height. You are already going to have huge climate control and comfort issues unless you hot roof it.

Where is the plumbing ?/ That will drive at least some of the ideas . A to scale plan is a must and in thta plan show where the plumbing is . How do you paln to use the space day to day?To me this roof/ veilung is overkill and actually imposes many issues into any plan Can we see the whole exterior and the house .DO yu need to bend down to look out those windows it appeas to be that but that is why we need info and a plan and ceiling heights

Are you on a septic system?

There are lots of layouts in house plans

That is not really that big of a space by the time you make it legally habitable.

The location of plumbing on the floor directly below this will probably drive the location of your new bathroom. Tell us that FIRST.

Agree with all comments - is this a whole house new build going up? I ask as I understand it’s pretty much a no go to add flooring / weight bearing structure in an existing attic over a garage post build. I could be wrong about that though. As to what you have, based on what my bonus room over my 3 car wide garage looks like, if those side walls are at least 5’ tall, your space is pretty usable. Seems like logical place for bedroom is at the end with the single tall window in wall. Having a window in the bedroom would be the best & it might also be code for an escape route. Of course the bath location depends on plumbing below.