I bought this wardrobe on ebay and have noticed that it is missing a top section. Can anybody advise where I might pick one up?

you could have a cornice/ canopy / pediment/ top / hat made by a joiner.

the wood looks mahogany

you could find some old wood, may be in that place the maise on Shakespeare Street or at Sutcliffe's on Linacre Street or even at Bret Griffiths West Lancs Antiques who advertises on the right hand side of the page.

I hear horrific stories of Rip off situations on ebay.

I always say if a person is not willing to put their name and address and phone number down then do not deal with them

good luck