So basically it's a case of putting one in which I think would really set the room off (top floor bedroom) or leave out. Leaving out would be better for warmth (in Wales) yet I worry that I might be missing out on the room ambiance which later would be difficult to correct such is the construction build. There would be sufficient light without one I think but I think it would definately bring the room alive. So just wondering if anyone has any experience with having roof lanterns? and any problems with keeping in warmth? 

In theory this shouldn't be much worse than any other window in the house. So unless it's enormous I would go for the ambiance myself.

Yeah, it shouldnt be enourmous,  looks like it will be just over a meter and a half (thinking of an octagonal one  ) so in proportion to the room

How will you clean the outside easily?

Algi coloured glass?

It's a flat roof - one capable of bearing weight. Additionally there are self clean varieties available - though I do not expect it to never need cleaning. Think I've heard heat loss can be greater though a horizontal pane than vertical which is why I ask? i.e if anyone has had rooms left freezing in winter because of roof lanterns. 

i intend to use a simple 3-glazed fixed rooflight:

• ext insulated upstands with fall
• triple glazed argon filled glazing unit approx 3m x 1m, top layer in 6mm toughened
• top glass sits on upstands, inner panes are smaller and sit inside upstands on supporting ledge
• rubber seals on supporting elements top and inside upstands
• £1300 inc vat
• I am looking for a simple alu trim to use as a drip: F-shaped moulding with rubber seal in mouth of F to clip over extended top pane of glass.