Where is the access point? How are you going to get up to this space? That will have a huge effect on how the layout can work. Also, window placement?

Agreed. Placement of doors, windows and stairs can dramatically affect the accessibility of the space. Would need more information before suggesting what would work best for a layout.

No it doesn't help. You need an architect, permits, an elevation/siting plan , a floor plan for the interior that best accommodates your needs. Nobody can provide answers online. Get pro help , ON SITE. A 250k addition deserves a decent plan. Everything else is just idle conjecture, wasted energy and time. All of it, yours.

Sorry but without even a floor plan how could we possibly know how to design a closet at all.

You need a minimum of 22 linear feet of hanging? A 5x8 is going to only allow you to hang clothing on 2 sides. Strictly double hanging the entire space would net you just less than 21 feet. If you can get a 6x8 you can hang on 3 sides, depending on the size and locations of your wall returns and door placement.

Interesting that you can only hang clothes on 2 sides in a 5x8 closet. I would think that you can use the wall across from the door opening for hanging also in addition to the 2 sides.

Two sides meaning the back wall and one side wall... Three sides don't work for hanging, as you need 2' clearance for a hanger to protrude from the wall on both sides plus a minimum of 2' clearance to walk. Mind you, we are going by a description, not a floor plan. If the wall is 5 deep by 8 long... then yes, you could hand on 3 walls.

This would give you 24' of closet space and still leave you with a massive bedroom...

Also, if you can avoid it do not put a window in your closet. It takes up valuable wall space....Best Wishes.

Windows in closets are awesome! It's like walking into a room rather than a dark storage space. And the light's always on.

One downside: if the window gets south or west direct sun, put blinds on the window so that clothes don't get faded by direct sunlight (I have a casual coat with a slightly lighter right shoulder than left one).

Windows in a closet are great, but I would double check placing so that they are on a wall that you won't lose too much space. Also they make a great divider for "areas" whether it's "his & hers" or "shoe & bag"and "hanging."

We have a very similar situation. We are putting in 18.5x22 studio apartment for my elderly parents attached to our house. I am trying to figure out where to put in a 6x8 walk in closet for all of their clothes.