From:  Daniele (BADANS)
1021.2 In reply to 1021.1 
Generally, to cap irregular surfaces like that, the best way is to break each edge in two halves and then run Loft with the two halves as input.
In this case the top edges were already divided, while I had to join the bottom ones and re-divide them 'cause the original breaking point wasn't in the exact middle.
Hope it helps
Happy modeling