I've been asked to modify an existing diagram of a building, and then to export it at a specific scale (1:50) so that it can be uploaded to a web portal.

The diagram was set to be 1 on screen unit =1mm by the person who originally created it. The overall size of the building in the diagram is 500MX500M

I create a new sheet and a new viewport, and set the Scale on the properties window to 1:50.

My screen then zooms right out so that the sheet is about 1cmx1cm on my screen, and the building in my diagram is so large that you can't even get one room on the page.

Can anybody help me to get the output that I need (A picture of my building as a PDF file in 1:50 scale, where I can see the actual details of the building)?

I am Using Draftsight 2016, and have almost 0 experience or training in using it.