Hi Team
Happy New Year
Do you want fitted storage or built in storage and do you want it to look like a piece of furniture or the alcoves just filled in.
Definition;
Fitted; a bespoke piece of furniture been designed and constructed to fit a given space that is totally free standing.
Built in; None furniture usually with no backs or sides just facia.
Shelves
No deeper than 250mm (10”) for books fully adjustable on book case strips this allows the shelves to be adjusted every 20mm (3/4”) unless you have very deep books then the shelves will need to be deeper but generally 250mm is just the job ( take a look at your local library )
If you have shelves any deeper 250mm for general display or storage then they will look totally cluttered and a complete mess.
Proportion
In general doors should be taller than they are wide and good proportions are A4, 8 x 6, 10 x 8, 7 x 5, 5 x 3 etc in other words 1: 125 ratio there or there about.
( think of photo frames )
Depth of cupboards
A lot depends on what you want to store or keep on them but a small traditional TV will need a service depth of 600mm ( 24” ) but for general use 400m (16”) is fine again if the cupboard is to deep it will be cluttered.
Consider the bottom cupboards to be drawers not cupboards but disguised as cupboards on fully extendable drawer runners ( better for storing toys etc.). Don’t forget there are no rule on the height of a drawer it is what is good for the purpose.
http://www.alanwakefield.co.uk/plasma pop up TVCabinets.html
http://www.alanwakefield.co.uk/large images/TV Cabinets/tv-dresser-4.jpg
http://www.alanwakefield.co.uk/cabinetry.html
Total height
In general fitted furniture can be the same height as the internal door 2000 / 2100mm or the height of the windows. This gives a clean line all round the room. For built in that’s up to you but it is better to go to the ceiling taking in to account any cornice in the room.
Ideas
Magazines & the web try asking Mr Google about fitted furniture then look for images.
A little later I will dig out a drawing of something I have designed in the past and publish it on my web site just to give you some idea of design.
One last thing it is always better to try and keep the fire place / chimney breast standing by its self just like SunnyUk is saying i.e. fitted furniture any Tom Dick or Harry can have built-in. But free standing or fitted furniture is a totally different ball game it shouts quality.