At this moment it is no possible to generate the TTF files (or any other format) from the geometry without buying FontLab.
I would suggest a possible workflow in which the font geometry is initially exported to a vendor-neutral format that preserves all FontLab information (I'd assume one SVG per glyph and text representations for tables and other metadata). That neutral format would then become the "source code" and a designer would work by importing (or assembling) all geometry and information into their preferred program via a script (FontLab, Fontographer, Illustrator, FontForge, InkScape) and then export the changed elements back to the vendor neutral format, ready for a git commit and a pull-request.
At this moment it is no possible to generate the TTF files (or any other format) from the geometry without buying FontLab.
I would suggest a possible workflow in which the font geometry is initially exported to a vendor-neutral format that preserves all FontLab information (I'd assume one SVG per glyph and text representations for tables and other metadata). That neutral format would then become the "source code" and a designer would work by importing (or assembling) all geometry and information into their preferred program via a script (FontLab, Fontographer, Illustrator, FontForge, InkScape) and then export the changed elements back to the vendor neutral format, ready for a
git commit
and a pull-request.