You may want to check your template file. It sounds like you are using a metric template, so everything will be in metric. You can actually just type 5', or whatever dimension you want to in ft and inches and it will convert to metric for you, vise versa is also true.
You can change the units without issue but all your families that are loaded will be the metric ones. So a 3' door will say 914.4mm or something like that. It is better to have a template for both metric and imperial and select which ever one you are using prior to starting the project.
Cheers Peter.
