Congratulations on your fort purchases, Giorginetto! I had one Fort Bravo as a child and purchased several others off of ebay recently. I created a Roman fort with them a couple years ago and it took up a lot of space. Unfortunately I didn't take pictures or measure it, but as I recall it was around 6'x10'. I've decided to use these fort parts for a Celtic hill fort instead and use the new System X wooden forts for a Roman fort. Unfortunately, I was unable to get most of the parts I needed for this from US DS, so my System X Roman wooden fort has only one wall right now. I also created a Roman fort out of System X castles.
Martin, unfortunately I don't have any directions for the headquarters, but the construction is pretty simple if you have all the parts.
It is tough to find the time for organizing and constructing all of these!