Mate I done ALL mine myself apart from laying the bricks. You may get it done for 10k but I'm telling you I had alot of help in skills, labour, freebies and cheap materials!

If its for 2 cars then the space is ample. But it will never be enough. You will always fill the space with spares, tools and crap and wish you went bigger. Go as big as you possibly can. With all the storage in mine I can get 2 cars in to work on, three at a push and thats with a garage that can accomodate 6 cars with nothing else!