I did this in my house 2 years ago. The sunroom consists of a 2 Velux windows plus surround uPVC windows and sliding uPVC door. I used Sunshine Ltd in Galway who did everything (all electric works, laying floorboards, installing a radiator, plastring etc) except they didn't paint the walls. It cost €22k. The job created a lot of dust which took weeks to settle. Painting the room and adding blinds cost more. Make sure that you price your blinds as there can be massive savings. I used Acme Blinds who have branches around the country.
When I was costing the job, I found that some companies expect you to get your own plumber, electrician, plasterer etc but it seemed like a pain the bum to me.
Also, I didn't require PP. I told my neighbours what I was doing before I started and they were all cool about it.
I hope this helps