A friend of mine did it with his transafrica Discovery - did away with the stock roof hatches (sunroofs) and fitted the biggest hatcvhes he could get to enable access to the roof tent and roof for game spotting. Worked really well and its stood the test of time - but it wasnt cheap at all.
As far as I can see the only reason Id contemplate it is access to the roof tent and the reason I havent is that I would have to substantially hack about and reweld my roof rack to deal with the big hole in it.... and Im not keen.
'91 LR 110 Def/Disco hybrid "Elsa"
Bring me the horizon....