I'm not a big fan of sliding doors for two reasons:

1. The view is slightly obstructed since the glass is not in one piece

2. More importantly: It's difficult to get things in and out of the cage. Would rather be able to open up the entire width of the front of the cage.

Have you seen custom enclosures with a full six foot pane of glass (it would actually be slightly less than 6 feet because the glass will sit in frame). The other option is plexiglass, but I think that discolors over time from the UVB.