The origin point of the curve plays a part. Set it to the topmost point in your example. Next the roof tiles object would have to lie horizontal not already pre-rotated. I’ve just used a simple subdivided plane as an example, with some faces cut out to show which end is which. On left are the plane object and curve object with no modifiers. The curve has been made straight to demonstrate. In the middle is that example with the Curve modifier. Now if I had already pre-rotated that plane to the desired roof angle then it would now use the curve modifier and rotate downwards even further. Example on right shows the same thing with a curved curve 
Ok, does the origin of the object matter as long as it is horizontal with the curve?
As for the curve, it seems to work better with the origin on the lower most end (opposite to where the arrows are pointing in edit mode) 
Can you expand a smiggen please? 
Try the lattice modifier, it will be easier to control. You can orient the cage before deformation.
You can also go into edit mode and use the Warp tool:
1: Place 3D cursor at desired bend pivot position.
2: Select vertices to bend.
3: Place pointer at the outer end of the vertices to bend.
4: Press Shift + W to activate Warp.
Hold Alt to make the bend affect the other side of the cursor as well.
I’m no expert on the Curve modifier. It confuses the hell out of me at times. There are loads of things that can impact the result: direction of curve, rotation of curve object (as in does it have rotation transform applied). I would just position the curve in the correct place for the final roof slope and move the geometry object until you get the result you want.
The advantage of using the Curve modifier over some of the other options is that it (in its default state) doesn’t stretch stuff along it. I’ve used it a fair bit for things like book pages where it performed very well.
In that example I had all the pages lying flat on the horizontal plane and the curve’s origins were at the point each page would emerge from the spine. Then I just had to move the pages around a little until each one just intersected the spine area.
