First off listen to Phil
But I'd like to add my 2 cents.
Here's some steps you need to take 1st.
How much power can you get to that garage? Find that out now, not when you order miners.
Do you have any type of neighborhood association?
Do you have a sound ordnance?
Do you have neighbors that complain or will complain?
Let's say you get past all that, like Phil mentioned you need to work on heat removal not cooling addition. Read through this forum there's all kinds of tips and tricks. I've posted some, but there's so many other more experienced folks who have as well.
Finally ask yourself some technical questions. Do you know what DNS and DHCP are? Do you know what a staic IP is? Do you know why you should run 220v instead of 100v for these things? Do you know what the maximum continuous load on a 30A circuit should be?
I don't care if you know these things right now or not, BUT before spending a lot of your hard earned money you should find out.
That's probably more like 4 cents