We did ours in 2021. We have one large bedroom, a smaller bedroom/office, lots of in built wardrobes and ensuite. Hip to gable and completely new roof bumped up the costs for us. Including everything eg plastering, flooring, bathroom suite, electrics, new boiler, all new fire doors etc it cost around £70k. We're SE London.
Definitely worth it for us - the extra space means we'll live here happily for many more years, (and the dedicated office space has been fab) but recent valuation shows that it's added more value to house than it cost to do.