Though I concur with Wyrmwood's answer, I am assuming you are talking about fermentation more than mashing and boiling.
But I would emphasize that it's important to have a stable fermentation temperature. That temperature can be low for some styles, but should typically be fairly stable, and preferably within the range suggested by the manufacturer for the yeast strain. I would follow package instructions on the yeast you get and find a way to stabilize temperature accordingly.
Preferably there would be enough ambient heat in your garage to stay in a tolerable temperature range. On the other hand, even if there is not, 20 liters of liquid is not going to change its temperature as quickly as a glass of water, much less the atmosphere around it, so you have some leeway. If the temperature shifts 5°C overnight, it probably won't kill your batch. Though, preferably, that shift would still be within the temperature range tolerated by the yeast.
So, I would say, take some measurements and, if they don't work, consider investing in temperature controlling equipment if you have a garage with wild temperature shifts. Another thing is, if you have to compromise a style a little by picking a yeast that fits your environmental conditions, it is almost certainly not going to have a meaningful negative impact on the outcome unless you are very picky.