creating a window seat in a shallow alcove ... how's it done?

[runningLou]

We are getting our kitchen redone and will be getting a new back door so have decided to get rid of French windows in existing dining room, which we never use. New kitchen will become a kitchen-diner and dining room will become back sitting room ... I would like to replace French windows with a window the same width and create a window seat underneath. The window alcove is only about 20cm deep currently, so too shallow for a window seat.
Is the easiest way to do this to build fitted cupboards / bookshelves on each side to deepen the alcove and then put continuous skirting round the bottom?? Would a carpenter be the person to do this?

I'd have some low storage fitted into the alcove - slightly petruding but not very much as seats don't have to be very deep - and make that the seat. Yes to fitting skirting around it at the bottom.

Yes that's what I was thinking, a storage bench seat about 50cm deep ... I just think the sides might need to be deeper as well? Could possibly create the same effect with a storage bench and two bookcases without having it built in (cheaper option)?

A dining chair seat is generally about 30-35cm deep so I wouldn't make a window seat much deeper. If you do, it won't be comfortable as your back won't be able to rest against the windows easily.

I wasn't thinking of resting back against the window, but against the sides ... this is why I'm trying to find a way to make the alcove deeper, like with bookcases (as in pic), as it's only 20cm deep at the moment.