Hi there,
Gone through the attached ppt and understood the requirements.
We can allow developers to create blocks, we would allow them to write chunks of HTML/CSS/JS separately, pretty much as it is on JSFiddle for example. I have not factored building a nice IDE but rather for plain textareas.
They could set the price for their blocks and select a category headers/footers/menus... then in the builder customers could drag and drop those blocks onto the "canvas" and build their website.
Please not that this will work, but developers creating the blocks have to cleverly name their classes.
Regards,
Julijan