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Massive differences. What's the substrate, what type of paint, how many square meters.
For a one off job you probably don't need a fancy frame but it might be worth getting a decent roller sleeve.
There are so many choices it's hard to narrow it down for you, I have at least 30 roller sleeves, 10 frames and maybe 10 buckets and trays. All to suit different circumstances.
The most general starter type for emulsion on walls would be a 9" roller and tray set.
I don't use the trays for whole rooms, I prefer a bucket and an extension pole. I would also stick to sleeves from brands like Purdy or similar but I get a lot of use out of them. There are lots of different textures to choose from depending on the condition of the walls.
Airhead-
Farrow and ball paint on a fresh plaster, large bedroom.
I've used budget stuff before but found that i'd always bend the frame or get a flat spot in the roller which meant the paint wouldn't go on evenly. In hindsight i'm probs bending the frame cos i'm pushing too hard to compensate for the flatspot.
Scunny
Is there a decent paint roller I should be looking for, or are they all the same?