There can be many unknowns and or hidden expenses when it comes to any new construction. I would always advise someone to seek professional assistance or consultancy from a builder. Searching for a local tradesmen and exchanging some phone calls or emails is usually a great start. To give an idea of a ball park figure reports of building 3 12×12 stables cost around £13.5K in the UK in 2007. Prices will be higher in today’s market so I would expect in the region of £15-20K.