I know someone who uses the following phrase: "that will be suffice".
Suffice is a verb which means "be enough or adequate".
So something cannot "be suffice". Instead it can suffice or it can be sufficient.
Surprisingly, a search on Google for "be suffice" returns over 88,000 hits. So this must be a common mistake.
Researching this did lead me to an interesting article on the relatives merits of "suffice to say, suffice it to say or it suffices to say".
Suffice it to say, this article comes down in favour of my preference of the three options.