Can you put a 11 foot kayak on top of a Honda Odyssey (2009) I think the roof is around 10 ft.

I used to top a 16' aluminum grumman canoe on
a 2001 Odyssey. You just need to have good bars,
or enough foam blocks for the gunnels. Tie down 
front and back, cross ties. Should be fine.

i had a 10.5 that i would top on my toyota camry.  i've seen plenty of vans and suv's with what look to be 12' kayaks on top.

your main concern will likely be the weight of the kayak and how easy it is to get high enough to put on top of the van.

can the yak hang over the front of the car and the back?

Just now, trick worms said:

can the yak hang over the front of the car and the back?

Sure. Just make sure you put a flag on the 
back of it if it extends more than a few feet.

I've had a 17' on a older model ford windstar. Went from the grill to past the back bumper. I do have a lot of experience tying stuff down with ratchet straps though so take that into consideration 

Up until november when I got a my subaru outback I was hauling my 16' sportspal on a Scion tC. I used a Yakima canoe kit with the foam blocks and three straps (front going under the hood, back going into the trunk and one wrapped around the center through the doors). Never had an issue. Snug it down tight and check the straps before getting onto highways.