Hi, long time no type ( I'm not dead!!) Moved house new railway room!! Shelving about to go up on one wall and the layout will be positioned under it 2' x 11' I need to fit overhead lighting to the underside of the lowest shelf, about 18" above the top of any scenic's. I looked at spotlights, tape lights, tubes, mains, battery or USB  etc .... Minefield!!! Any advice would be much appreciated

Cheapest and easiest install are the mini LEDs that come on a self adhesive roll.
Can be powered by (almost) any smoothed DC supply and if you use a variable supply can be turned up/down to suit.

Do experiment with the number of strips and different "warmths" I.e. colour tones/casts, and mounting at different angles to see what works best for your location as background conditions can have a noticeable impact.
Our exhibition layouts now generally have 3 or 4 strips including at least one each of a blue tone and a yellow tone all independently variable.

There are loads of cabinet / under-shelf LED lighting units / kits available.  Have a look round your local DIY store and lighting shop.  Lidl, Aldi etc. have them from time to time. 

Here I've used a pair of Livarno units from Lidl on the lighting rig for my loco depot modules. These are proper sealed units with diffusers, mains powered and daisy-chain-able.  I have another 4 units ready to replace some old reading lights on my main layout's lighting rig.



A fabric pelmet goes around the outside of the rig at shows.