First off, welcome aboard.
Secondly, there are many books out there, some of them fairly recent, that will really help you model these cars. I have one i just grabbed to find the answers you seek. It is called "Bridgton and Saco River Railroad Freight Cars" by Peter Barney. It was published in 2005 and spiral bound. Peter has found some excellent examples to look at, as well as some close up rivet counting shots.
Unfortunately, I don't see a drawing for a 30' car. But the 28 footers were 8' 11.5" from the top of the railhead to the top of the roofwalk. The 34" cars were 9' 1.75" from top of rail to top of roofwalk. They show no measurements for the doors. Hope this helped.