Since I discovered the Natura Redwoods I've spent (at first) hours looking for one on a new world in "cheat" mode. Now, if I'm in a hurry I just give myself 81 saplings. I use a 9x9 grid instead of 7x7 because the tree seems to grow faster, which I've been told is because a 9x9 contains multiple unique 7x7 arrays.
Also, There are several sizes of tree I've seen, from 13 blocks diameter down to 9 blocks, and the 9x9 array seems to grow into a 13x13 mostly in unleashed. In Direwolf20 I usually get an 11x11.
Another small advantage... Doors made from the Redwood bark are named "Secret Doors". This works when the door is used on the tree... Haven't had a midnight knocker yet. I don't know if it works on other structures.
I usually hollow them out, leaving the central block intact as a ladder support so I don't have to shift the ladder around as the diameter tapers. I also dig straight down using the same column to below root level, at least to y:50, and build out a room in each of the 4 directions. These contain my Foundery in one room and magic room opposite, and ore berry farms in the others with room to expand downward.
Note: this build is about a week old. There are only 2 above ground levels so far. The clear glass is from the Tinker's Construct smelter.
[edit] I should also add that I use smooth stone half-slabs as my floors to prevent Endermen from teleporting in on me. Early on I had a bad rainy night with the Enders... It also allows me more wood to use instead of walking on
