irregular frame grid

good afternoon

i have a facade already divided in parts and what i want to do is to generate a random facade division from the regular division. By splitting the list of windows randomly and after that joining it and using the boundary line for generate the frame(50x50 cm).

The problem are:

1. planes don't come aligned to surface. 
2. the use of offset curve doesn't work because in some cases the curves belong to different planes.

any idea how could i achieve what oi want

thanks in advance

Roger