The big problem with solar lighting is that you get the least power from solar when you need the lights the most, so you need a big solar panel for winter which then generates far more than you need on the summer.
My local electrical wholesaler sells a 3watt (equivalent to ~30W normal bulb) solar PIR security light which is a complete unit with a separate solar panel attached by a length of wire for about £90; and a 6W version for about £110 (+vat). But the battery is quite small so I'd guess it would be only good for maybe 2 hours tops from a full charge, and in winter it may take a full sunny day or a week of dull days to fully charge the battery.
A cheaper option if you need minimal light is a few of those solar garden lights with the panels detached and placed on the roof (and if your electrical knowhow is up to it a switch between the battery and the LED driver so you only use the battery when you want light).
If you want serious light and/or extended daily runtime in winter, then you would be better with a 12v leasure (arguably) battery, a 'proper' solar panel (50W or more, depending on usage), a solar controller/regulator, and some off the shelf 12v LED's (like the LED substitutes for 12v halogen lights). Also can be used as a power source for electric fencing (though add another 20-30w of solar on top of what you want for lighting).
there are some 'kits' about like these:-
http://www.sunshinesolar.co.uk/khxc/gbu0-catshow/solar-lighting-kits.html?gclid=COrTgNyel7oCFQTMtAodC0MA3wbut they seem expensive to me, compared to buying the separate parts elsewhere, and are short on details. If you do find a kit that seems to suit, ask them how bright the lights are, how long the battery will run them, and how many dull midwinter days it would take to fully recharge the battery.
without knowing how much light, how often and for how long, it's difficult to give specific suggestions.