Ask HN: Guidelines for building an “app builder”

Hi there HN, I am a 4th year computer science student, working full time as an iOS developer currently. Off the job I want to make an "app builder". What this means is I want a WISWYG app builder for non-programmers to be able to build somewhat complex apps for iOS and Android without any prior knowledge. This will all be done as a web app in browser.

There currently are some app builders out there but most of them I feel are really hard to use, or provide with very little functionality.

What I aim is to have as many templates as possible. By templates I mean things such as Login/Register forms which users can just drag&drop into their app and customize afterwards, with the DB and functionality being already made for them in the background. Another really good feature would be a user being able to upload the source code to their website and the appbuilder would then be able to convert that website into a fully functional app, which they can then modify to their needs.

My experience so far is based on some web apps, Android and iOS programming. For this reason I ask you the following questions:

1. What programming language should I go about using to make the task in hand easier to handle? I do ask this because I don't really have alot of experience in any of them, but I am a very skilled googler so I don't imagine having a hard time learning whatever you suggest.

2. How should I go about designing this?

3. Any tips you might give me to start this up

4. Any example "app builders" you can provide which you find have something awesome in them, and what exactly is that something awesome.

This is the first HN post, but I aim on making some sort of written progress on my programming maybe in the form of a blog. This is considering I am aiming for an open-source app at the end. Thank you for your patience