I'm going to put Pot's Lane into an urban setting, surrounded by a retaining wall and the street behind. However, the station entrance will be at steet level, with the platform below  and will have a lift shaft on the side for trolleys etc. My question is, what's the best of laying out the station building. Would it work if I had a "normal" station below with a similar up top but reversed?  

Not sure if these help, but there are a few layouts on here that have the high street scene and railway below within retaining walls.

Here is a selection to look at :

Aaron's layout Kingsmead : http://yourmodelrailway.net/view_topic.php?id=10669&forum_id=21

Andy's Lydford Road : http://yourmodelrailway.net/view_topic.php?id=7192&forum_id=21

John's Scalescene diorama : http://yourmodelrailway.net/view_topic.php?id=8116&forum_id=21

Pauls layout Cannons Lane : http://yourmodelrailway.net/view_topic.php?id=10474&forum_id=21&page=1

Cheers, Gary.

Thanks for that. A big help.