Questions & landscape sketch

Hey guys,

If you have any questions relating to construction, materials, methods
and etc, please reply back with them so I can compile them together and
send it to Udoka (our contractor and friend :) ). Also feel free to add
questions you've mentioned during our discussions but I've have
forgotten to include.
Also, I've attached some images of the latest Sketchup model including
an iteration of the courtyard area. I was exploring the concept of
creating a landscape with cylinders that can be stacked upon one another
to varying heights. The kids can jump around them as they please as
well as provide seating. Thinking about it further, possibly each unit
can maybe have a name embedded in it representing the support from our
financially providers. I'm open to ideas, comments and etc.

1. What is the maximum height for a column to support a roof
structure within normal construction methods? Can you provide the
maximum heights for a steel column and concrete column?

2. What are the maximum spans a wood truss that can safely
achieved and are within normal construction methods?

3. Are polycarbonate (plastic) roofing materials available? How
much for a typical sheet and what is the size of a typical sheet? What
colors are available? Are there ones which light can transmit through?

4. What are typical window sizes (glass) that are available? How
much do they typically costs over in Owerri (or locally)?