Conservatory type Extension as a pool room

I'd like to build a conservatory type extension onto the back of my house, so that I can get a pool table for my house! Looking for recommendations about the right way to approach this and good building contractor companies to deal with.

I'm located North Co. Dublin, 3 bed, 2 storey house. Currently on the ground floor, I have 2 large double glazed patio door rear entrances, no rear windows on the ground floor.

Want it to be approx 30 x 18 ft and allow as much of the current light at the rear of the house to still enter. Is it feasible to have a glass roof over an 18ft span? I’m guessing it’s too far... What might be the best roof solution in this case?

I’ve heard some horror stories about some small to medium sized ‘building’ contactors. Slow project progress, men not arriving on days that they promised they would, substandard work to highlight that they truly don’t care much about the customer etc.

Is planning permission required for an extension/conservatory? I’ve heard that you may not if it’s at the back of your house or that if it’s not a ‘permanent’ structure. Maybe conservatories are not classified as ‘permanent’ structures?

I‘m interested in any advice, recommendations or stories from other people who have built similar type extensions/conservatories please.

Has anyone used Shomera http://www.shomera.ie/ or similar companies? They seem to do nice ones on their website, but I don't know if they're much good or not.... Any feedback on what they’re like; quality, timescales, prices etc. would be much appreciated.