Beginner's questions - Loft?

 From:  ClosedCircuit
6642.1 
Hi,

I'm a true beginner and have some very basic questions for a kind soul to answer (I know that google is my friend - supposedly, but there is so much material out there that it is sometime difficult to know which strategy to adopt).

I've started modelling a simple case for an HTC One and I'm not sure how to proceed next. The sides of the phone are at an angle, the corners are all rounded and the surface at the back of the phone is curved along both axis. So far, I created some ribs (in Red) and the contour of the phone (in Blue).

I thought that I could use Loft (selecting the ribs and the contour) to make the shape a solid, but nothing happens if I select Loft / Normal / Auto and I get some weird results if I use "Loose" (see picture).

I would really appreciate if someone could please point me in the right direction... The objective is to end up with a shell that can be 3D printed.

Many thanks!

Phil