Disco's are very prone to rot all over - areas particularly prone are the boot floor and the rear arches. The sunroofs always leak (there are 2 of them) most of them will be sealed with sealant but still leak from the surround.
Have a look on Landyzone.co.uk and you will see a few of the common problems on there and there may be a buyers guide.
On that particular Disco in your link it looks like someone has modded it up to be a mud plugger so maybe view before you bid as it may have been battered round quarries and fields. Wipers are not parked properly so could indicate electrical problems,
All that said - I have a 4.6 V8 Range Rover and love it to bits, bought it as a 3rd car but I always pick the keys up if popping into town, 12MPG is a bit frightening but that aside it's a great car.
Darren