Steven, for my model, I've found that actual dimensions are very scarce. I have been using deck plans and general arrangement plans for horizontal dimensions and measuring them with a ruler in millimeters - the scale of one of my larger deck plans is 1 foot = 1mm, very convenient. Seems to be working quite well.
Vertical dimensions are a much different story and are pretty much non-existent. I've used lots of methods to estimate those and have been pretty successful. I can relay them as you would like. Feel free to send me a message via the Forum.