My girlfriend and I are house hunting and one house we looked at had a pretty nice block/concrete built workshop at the bottom of the garden that would be an ideal man-cave. The rest of the house didn't tick all the boxes though, so I'm wondering if any of you have built or had built any external buildings with power etc. that would be useable as a secure office (I'm thinking more brick/breeze block/concrete than wood as I'd like to insulate it and make it theft proof to use as an office as well as place for my layout).

What sort of cost am I likely to be looking at?

It really depends on how much of the work you do yourself..... I had a garage built about 10 years ago and had all the work done by a local trusted builder. I asked for 3 different quotes to get a handle on the price. My small local firm were the best. It cost about £8k to dismantle and remove the existing sectional concrete garage, smash up and remove the concrete base, dig out new footings and base and build the garage. Unfortunately the builder is no longer with us, so I can't use him again.

Being brick built it will be a 'permanent structure' and as such would need to meet building regulations and maybe even need planning permission. A chat with the local planning people would be my first point of call.