No clue from the little info you have provided. Exterior shot? Plumbing able to get there? What are you thinking budget wise (guarantee you no where near enough)? Minimum 75K if it is even possible.

Since your layout is unique and remodeling costs vary so much from region to region, you'll be best served by asking local remodelers-- not crowd sourcing the question here on houzz.com

Best wishes for a successful project.

I would need to see the whole floor plan in a to scale drawing the big question will be the plumbing and your budget.

The national average for a bathroom addition is 87K. You are proposing something a lot more complex than a straightforward addition. You’re proposing beefing up a storage second floor to live load requirements and rebuilding the entire roof in that section, not just a dormer. You could probably add 50% of that 87K as a complexity premium, and then adjust to your location premium. https://www.remodeling.hw.net/cost-vs-value/2019/

I have no idea wether this is a attic space or an actul living spce now , As for touching the roof when we wanted to add a skylight to an old house were were told that if we touched the roof we would need to bring it all up to code so no skylight for us.

Where do you get 87k for a bathroom? Sorry, I can't take that response seriously. That's not the national average. National average is closer 10 or 15k. This says 25k is the upper reach: https://homeguide.com/costs/cost-to-add-a-bathroom I suppose you could spend 90k on a bathroom if you wanted to ,but that's not the national average.

If you look at the link posted, the 87K is for an upscale bathroom addition.

In your link, the 25K is for a remodel.

Comparing apples and oranges. "Upscale" is a HUGE factor. In the first link, a midrange remodel is 20K which is probably closer to what your link is describing.

These averages are useless anyways. So much depends on your location and your specific situation. Your situation is somewhere between an addition and a remodel since it involves changing your roof line.

Spend a little money upfront to get a designer on board, then have a couple of contractors price out the plans for you. You can save money if you buy all the materials, but the biggest cost will be in the labor to build it out. Bathrooms and kitchens are typically the most costly to remodel since you're literally using every trade out there: carpenters, plumbers, sheet rockers, tile installers, electricians, cabinets, and slab fabricators for good measure. And depending on how busy contractors are in your area, there may be a premium built in because of the demand.

So, the answer is there's really no good way to estimate this project until you have plans because averages are pretty useless and construction costs vary so wildly from geography to geography.

I find the cost data in Remodeling Magazine's Cost vs. Value Report useful for calibration purposes; particularly for folks who've been fed a diet of mostly HGTV. For example, if someone is expecting to spend $10K to make a bathroom appear in a space with no existing plumbing or electrical they can forgo the expense of producing plans or bothering local pros or they can call Chip and Joanna "Shiplap" Gaines.

I would caution folks about purchasing materials for a project or at least making that intention known to prospective remodelers before taking up any of their time. I think you'll find it will narrow the number of prospective remodelers, particularly in a good market.

if you are intending to build this for yourself , in your own home, approximate cost 10k. it does not include tools necessary to accomplish this task.

if you are taking this one as a project for someone else i would charge around 22k easy

I can only speak of projects we have done. A REMODEL for a bathroom is typically 20 - 25 K for labor and materials. A completely new bathroom in a new space will require permits and and architect and will add 10 - 15K to that project. You are also talking about altering your roof line - throw some more money onto the pile.

Your first step is to get a local qualified contractor to come in and take a look. Depending on the dimensions of that area it may very well be possible to do a bathroom in there without having to deal with the roof.

Hope that helps!

some of you guys are forgetting about the roof. OP has provided no info if taking up the roof can be seamlessly joined to what's there, and patched in. ( permits, drawings and actual roofing, could easily come in at 10K)

We have no idea about the plumbing and sewer lines for that part of the room. again, permits, plumbing.

electrical? see above

second story? tile is a lot heavier than what is there. expect to fortify any joists.

HVAC? ductwork

All of this ^ and we haven't even touched the materials and labor that actually go into making the bathroom.

Also, have no idea where you are located. NYC gets much higher prices than rural MS.

Typical bathroom?? what's typical? builder basic? DIY tiling? neighbor Bill's labor or Certified Tile Setter? Nice quality materials or sale bin from Home Depot?

How can we possibly answer your questions?

You can figure between 25K and 75K. that would be a safe estimate. You're asking the wrong people here. you need professionals in your area that can actually see your home and roof and decide exactly what's what.