Good idea with this thread, Andail.
Ok, I also have a problem, this time I need some perspective issues. I can't explain it by words (due to my poor English*), so I've drawn a schematic picture with a simple room on it and the one reference point. That window and the cube no. 1 were easy to draw, but when I had started drawing next cube with -probably- another perspective point, the trouble appeared.
So let's face it...


The cube no. 1 is parallel to no. 2, the same for the edges. The "top view" box illustrates the relations between both cubes and room's walls. The question is following: how to draw the cube no. 2?
Hope it's clear to you.
*One of the reasons, why I've decided to sing-in and join this community is to improving my English skills, so...
If you have a time and alacrity, please correct my utterances (as quotes, or post-edits),
where it's necessary. I wish you do that with every post, that I will write, but it's probably impossible.

Anyway, I don't want impose this upon you, so I count only on your good will. C ya!