House Extension - where to start?

antilles

Girlfriend bought her current house around a year ago and she is looking to have a 2 storey side extension added (there is plenty of land around the side of the house for this). Originally we were going to leave this for a few years, but I also still have my own house so we are thinking it would be ideal to have it done ASAP while we have the option of staying at my house and leaving the builders to it.

We have a pretty good idea what we want so we are currently drawing up some basic designs on graph paper. She also needs to call the bank this week to see if we can part finance it by borrowing more money on the mortgage.

I've done a little bit of research but am not 100% sure where to start - assuming she gets OKayed for the extra cash, I assume we need to hire an architect, get planning permission, then hire a builder.

Are we best just getting a couple of local builders around for a ball park quote/figure before we do anything?

Would appreciate any advice on the 'correct' order of things from anyone who has done similar.

Also, are there any rookie mistakes which might catch us out during the process?

Thanks