Wooden shelving for an alcove

[elsmore1]

Hi,
We have a small alcove area were the corridor ends adjacent to 2 doors which is about 3 feet wide the width of the corridor. Similar to an area between a fireplace. As its a bit of dead space we plan to add some shelves. I fancy tackling this myself and wondered the best way to construct the shelves, my wife does not want the metal shelving system so it must be wood. I am planing to use wood of 18mm thick, not sure best type maybe blockboard or MDF? Any recommendation on depth it will be used for books. Is it best to have wooden supports all the way around i.e 3 sides and then piece of wood on the front to act as a support too and to cover the other supports a bit. It is a plaster board wall as modern home so what would be best fixings or any websites to point me to to give pictures. I have done my research from the Collins DIY book which has proved helpful in the past. My main worry is the shelves sagging so is 3ft too wide will I need to support it, maybe borderline size.
Thanks

 

[Burnerman]

Just for a kick off.....visit the DIY sheds and see what they have ready made.....for example, they do pine boards of a variety of widths and lengths, solid and machine sanded. These save using a timber lipping that you would need with ply or MDF. Granted, its a bit more expensive but looks well right from the start.
Depending on what weight you intend to load on them, a 3 side support would be needed, but for short spans two bearers would be OK.
John