- attic/loft with huge windows for natural light (skydome  and hdr practice)

- interesting ceiling shape

- big comfy bed in the centre of the room as the main focus (possibly with 'floating platform to have fun with light)

- built in bookshelves for decoration

large house plants

- white and cream or white and grey colour scheme (possibly wooden beams)

- clean and simple look (less clutter and personal items)

- simple modern designs for furniture (blocky bedside table and bed frame)

bed

bedside table 

shelves

arm chair

ottoman/poof

rug

mirror/large round wall art

lamp

large house plants

books

small statue (bookshelf)

desk and chair

staircase

                

References

Rug - https://www.cgtrader.com/items/2555861/download-page

bed 1 - https://www.cgtrader.com/free-3d-models/interior/bedroom/black-bed

bed 2 - https://www.cgtrader.com/items/2078747/download-page

armchair - https://www.cgtrader.com/free-3d-models/interior/living-room/medium-white-armchair

small table - 

long table - https://www.cgtrader.com/items/2199733/download-page

desk - https://www.cgtrader.com/free-3d-models/furniture/furniture-set/archmodels-149-set01

drawers - https://www.cgtrader.com/items/178295/download-page

frame - https://www.cgtrader.com/items/3423044/download-page

décor - https://www.cgtrader.com/items/2173026/download-page

books - https://www.cgtrader.com/items/200467/download-page

plant - planthttps://www.cgtrader.com/items/3151361/download-page

staircase - https://www.cgtrader.com/free-3d-models/exterior/industrial-exterior/aluminum-spiral-staircases

lamp - https://www.cgtrader.com/items/2706161/download-page

I'm going to replace the cylinders with chairs and puff and a long short table on the side to fill the awkward space.

I might add some furniture to the other side of the room to make it more realistic.

I'm going for a simple/minimalistic room to keep that clear and functional use of a bedroom so there wont be too many pieces of furniture or clutter.

I also added exposed beams to emphasise the attic look.

I ended up adding a spiral staircase as this is a bedroom attic and there's no doors so there needs to be an entrance.

the staircase makes it a little more interesting.

I also found a bunch of small décor pieces to decorate blank surfaces and a large monstera plant

Here's the first render of the scene

I added lights on the walls as it's difficult to have a ceiling light but the giant windows make up for that. I also added lights under the bed p[platform to draw your eye to the bed as it's the main focus of the room and it also looks cool.

After placing the camera I realised it's hard to get a good shot due to the size and shape of the room. I can really only take the render from one angle.

Here I changed the layout of the room a bit as I could only render the scene from one angle and it bothered me a lot so I added a wall in the middle of the room to divide it into two separate areas: a sleeping area and a sitting area.

I also added glass to the windows and remade the walls and room as it was very messy. I changed the supporting beam and only added windows to the left side of the room. I also added a desk to utilise the space better.

In this render I added photometric lights to brighten the room a bit and not depend on the natural light from the windows to lighten the scene. This allowed me to control the shadows and dark areas better.

I rendered the scene from a different angle to show off the sitting area. However the lighting was all wrong and it took me a lot of renders and tweaking to find out what was wrong (turned out to be the exposure in the camera settings not the actual light) But due to the position of the skyedome the blue tones and natural light looks better in the bedroom (main render) I couldn't get the same affect on the other side without changing the light in the main area. 

The sitting area looks very plain and white so I added a lamp to provide some warm lighting and moved the chairs closer to the centre of the room as they were clipping the wall and realistically no one would be able to sit there. I also added window frames.

Here are both areas rendered with and without atmospherical effects. 

Here is my scene with all models textured

Renders edited in Photoshop: