Window reveal advice

[vengenerator]

Hi there,
Hopefully someone can advise me on the best approach to tackle my window. Just decorating my daughters room in our new house and decided to remove the fairly nasty plastic trim that was around the double glazed window.

Whilst I could fit some more plastic trim I would really like to smarten it up a bit. It looks like this:

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As you can see the sides are conceret blocks and the top has a gap about 2 inches wide. If I look up into the gap I can see into the eaves, you might just about able to make out here:

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I first thought to plasterboard around the whole window but on testing how this would look with a piece of board I had laying around I found that the space at the top of the window is very shallow and also rather uneven so it looks pretty naff:

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So my current plan is to try this:
1) Use expanding foam filler to fill the gap at the top of the window
2) Go over the side area with hardwall
3) Skim the top and sides with finishing plaster

Is this a sensible plan?
Should I use the metal corner edgings around the reveal when plastering?
Is there a better plan? (i've never plastered before but am game to try)

Thanks ever so much for any advice. Originally was just going to paint this room and ended up stripping off all the badly bonded previous paint and now the window ho hum never as simple as you think!

 

[stevethespreader]

if that was my window i would float the reveals then anglebead up and skim the whole wall then replace the plastic beading job done

 

[vengenerator]

Hi Steve,
Thanks for the reply - excuse my ignorance - but when you say float the reveals do you mean put plasterboard up top and sides?

I thought that at first but if I board at the top the plasterboard comes down pretty much to the top of the glass - as in my 3rd pic. Thought it might look a bit weird if I did that - that's why I was thinking about using expanding filler to try and get the top reveal as far away from the glass as possible without mucking aobut trying to make the opening bigger.

 

[stevethespreader]

Hi Steve,
Thanks for the reply - excuse my ignorance - but when you say float the reveals do you mean put plasterboard up top and sides?

I thought that at first but if I board at the top the plasterboard comes down pretty much to the top of the glass - as in my 3rd pic. Thought it might look a bit weird if I did that - that's why I was thinking about using expanding filler to try and get the top reveal as far away from the glass as possible without mucking aobut trying to make the opening bigger.

no i would float with an undercoat plaster then i would put some beads up and skim the whole wall and you will have to replace the plastic beading with some fresh beading to cover the gap on the lintel its an easy job for one of us but not for a beginner