Interpolate mesh surface between curves Suppose I'm trying to model a curved surface: the roof of a car is a perfect example. Many tutorials suggest creating a plane mesh, which I should subdivide via loop cuts, and then proceed to model the mesh in two dimensions (say from the top, so X and Y). After that, I switch to a front or side view and I move the outer vertices along Z. 

Here comes the tricky part: I end up with two "edge curves", two outer profiles of my surface. Say we're looking at a side view, so the Y axis is along the horizontal axis of the screen. How can I move a "row" of vertices (vertices that share their X coordinate) or multiple rows so that they fit the smooth transition from the "back" profile to the "front" profile?

I know in a sense this sounds like lofting - it probably does, but I'm not sure I get the concept fully. However, I'm looking for something that I can apply at will, not only when creating and developing a surface. In other words, if I move a vertex of one of the "profiles", I want to be able to reposition the inner vertices smoothly based on the new position of the outer vertices. 

EDIT

Here are some screenshots to help you understand what I mean. 



Here's a plane mesh, with subdivisions in (supposed) key points. I move the outer vertices to match the surface I'm modeling. This is still a flat surface, but you can already see what I mean: I want the inner vertices (those still lying on the square grid) to be moved so that the rows transition smoothly from the curve of the top row to the curve of the bottom row. The "columns" should do the same. 



In this second screenshots, the outer vertices have also been moved along the Z axis. You can see what I mean by "smoothing the surface": the inner vertices should follow a curve so that the surface is smooth.
I think what you want here is the Grid Fill tool. 

Make your two profiles (make sure they have the same number of vertices), then fill them in with Ctrl+F > Grid Fill. 
Make sure you have Tools menu opened (you can toggle it on and off with the T key, it shows up on the left of the 3D viewport) or press F6 after command execution and you can fiddle with the settings; I recommend you using a very low setting and then use loopcuts. 

The cuts will have the right shape, so all you have to do is push them up or down the opposite axis from your main profile shapes. (If it was a floor or roof, this would be Z, a wall would be either X or Y.)