Roast the heads whole to save time. (Contrary to the typical approach, roast at 350 instead of the oft-used higher temps. This will give you full roasted flavor and texture, without the little hard parts and/or bitter bits that can result sometimes when garlic is roasted at higher temps.) You can put them in a roasting pan, drizzle with oil then cover tightly. Roast till tender, usually about an hour depending on age and size, then remove from the oven and allow to cool.
Using a sharp knife, remove the top quarter or so from each head then squeeze the garlic into a bowl. (Add the garlic from the head tops you remove, or use that in something you prepare today - or whatever day it is when you roast.) Mash the garlic well with a fork (you can purée if you wish - I usually do not bother) then transfer to a freezer-appropriate storage container that is just large enough. Pack well and freeze.
To use after freezing simply scrape the top of the frozen garlic to remove as much as you need, returning the remainder promptly to the freezer.