Ian, I thought you did blinds. Did a flood job for a blinds guy a while back, he was 54 and retired and he was telling me he made up to 700% marging on conservatory blinds 
A very good profit can be made on Conservertory blinds do not think 700% even if he manufactured and installed.
But if you can hold your Margin its a nice earner like selling a truckmount is
A mate of mine on the small blind Forum I am on restricted access only just 10 members so we can really discuss ideas is considering specializing in Conservatory Blinds and droping all the smaller stuff.
The hard bit is getting the angles right on the roofs a mistake costs dearly