Please help me as I haven't a clue what to do or how to go about it. ive attatched a picture of what i would like to build in my bedroom (in the simplest, easiest and cheapest means possible please!)

In my room i have an alcove (formed from the chimney breast in the room on the other side) and then i have my window, not another part of the wall like it is shown in the image. I'm not particularly fussed about having a 'roof' to it as i have a picture frame circling the whole of the room at about the same height as the closet, in the image, cuts off.
Phew.
I really hope this is enough information! Also, i live in the UK so if anybody answers (thankyou in advance) from outside, we probabaly wont have the same diy stores as you xD
Hope you can help!!
