Haven't seen the movie yet, but I am currently reading the e-book, and searched through it for occurences of "Israel" and "wall"...
The book only refers to a single wall, and it is vaguely implied that construction started some time before or just around the time of the outbreak of the zombie plague. It might have originally been intended to defend against Israel's neighbors or to keep out illegal immigrants, it doesn't mention its height. The following quote is from the recollection of Saladin Kader, a Palestinian entering Israel at the time the disease was just starting to spread, but still in relatively small numbers and most of the public not aware of its severity:
As we approached the border, I saw the Wall for the first time. It was still
unfinished, naked steel beams rising above the concrete foundation. I'd known
about the infamous "security fence"- what citizen of the Arab world didn't - but I'd
always been led to believe that it only surrounded the West Bank and Gaza Strip.
Out here, in the middle of this barren desert, it only confirmed my theory that the
Israelis were expecting an attack along their entire border.
Note that Kader is portrayed as being strongly anti-Israel at the time, and he wasn't aware of the existence of the zombies yet - or at least he didn't believe the rumors.
The same person about the location of the wall (emphasis and [editing] mine):
In your opinion, what do you believe was the cause of that war?
I think there were many causes. I know the repatriation of Palestinians was unpopular, so was the general pullout from the West Bank [...] Al
Quds [Arabic for Jerusalem], I believe ... that was the final straw. The Coalition Government decided that it was the one major weak point, too large to control and a hole that led right
into the heart of Israel. They not only evacuated the city, but the entire Nablus to
Hebron corridor as well. They believed that rebuilding a shorter wall along the
1967 demarcation line was the only way to ensure physical security, no matter
what backlash might occur from their own religious right
This is a confusing statement, as the border in 1967 (after the Six-Day War) was not shorter than it is at present at all, but included all of the Sinai, Gaza, the West Bank and the Golan Heights. So my interpretation of "1967 demarcation line" is the border before that war, more commonly known as the 1949 demarcation line or Green Line.
How long it would take to build such a wall is difficult to tell; I don't agree with Compro01's assumption that this wall would have a construction rate similar to that of the Berlin wall. The longer a planned wall is, the easier it becomes to assign more workers and to complete longer stretches of wall per day. Still, months to several years seems a reasonable guess.
However, in the book, it does take a while for the disease to become a global catastrophe. Early outbreaks were small and could be contained most of the time. With Israel imposing an early "voluntary quarantine", and having dogs at the border that could sniff out the contaminated so nobody would turn zombie once inside, it seems fairly plausible to me that they could buy enough time to complete the wall.