Boxing in Bay Window

[scouseman]

I am renovating my house and need some suggestion for the best way to case it my bay windows, currently it looks a mess.
Any advise would be most appreciated, I am looking for the best possible finish.
Thanks
Here is how it currently looks:



And this is the concrete behind the board:

 

[foxhole]

Useless photos , just show a dark surface .

 

[scouseman]

I should have shown a wider view photo as well.




Its just the two visible spaces that need to be filled as the other edges of the 2 side widows the plasterboard buts up against them.



Hope this make things a bit clearer
Sorry for the lack of better pictures.
Thanks

 

[Odds]

Have you thought about the finished affect you want to see?
Are you going to paint the surface or leave a natural wood on show?
How big a budget do you plan on using?

 

[scouseman]

Thanks for your response, my initial thought was to take my angle grinder to it and cut out a section of the protruding concrete, but the amount of dust that would recreate would be somewhat troublesome and possibly weakening the bay window. Although If I cut away the excess concrete it would look so much better as I could go straight across between the 2 windows with either plasterboard, plaster, paint or UPVC for a white plastic finish. As far a I can see and can alternatively go around the concrete with a 90 degree corner out of either plasterboard, then plaster and paint or maybe a flexi-angle https://www.trulypvc.com/building/exterior-cladding/upvc-shiplap/flexi-angle-corner-trim-5m , but I certainly feel this would be the easiest but certainly worse of all the options. I don't really have a budget I will need to weigh up the finish / cost ratio and I am certainly open to suggestions. I also thought about a natural wood finish to go with the bay window cill I will need to do, but I feel the concrete will still be an issue unless I cut it out.

Thanks again