Most attics are suitable for conversion and it doesn't matter if you have a truss type or hip type roof. What really matters is the height in the middle of the attic. This is a personal choice for the customer as to their attic conversion needs. 

Some of the lowest attics we convert are five foot from the top of existing ceiling to the bottom of the rafter in middle of the attic . This is quite low but suited the customer for their loft conversion requirements.