Steam Question

I do this exact thing. They have crazy deals over Christmas and I usually buy a few or several games. They also have summer deals going on. This is the beauty of Steam. Once a game is purchased it is on your list forever. You can download it as many times as you want whenever you want. They also have a backup feature so you can backup to a file and place it on another drive or external drive to save place on your primary drive (very helpful if you have an SSD). This is helpful so you don't have to download it again if you intend to play it down the road. Just buy it and download it when you are ready. You can also install Steam on another PC and as long as you are signed into your account you can download and play those games on that PC. Just remember that you can only be logged into one PC at a time with your Steam account.

Get the deals when you can.

You can purchase the games through their website, as long as you have the account. Then after you're done with building your PC, you'll load steam on it, log-in and all your games that you bought will be there in your library.

If you already have a computer NOW, you can purchase games from the Steam platform. Later, when you've built your NEW computer, you can login from the new one and your 'list' of games will be available on the new one. You can simply download from there. On the old rig, you'll but obviously be logged out, so your only session will be from the new rig.

You have no worries!   Buy them now if you want coz the deals on Steam are awesome!! I've ended up buying some titles which I already own through retail.