If your growing for height and you still want yield then id suggest going vertical.
The trouble with tall plants indoors in a traditional grow is that the light really only plays its part on the top foot of canopy. Going vertical will allow the height you want and still achieve a yield.
There is a vertical section in the forums, perhaps check it out.
I get nice Bud right down to a foot or so of the bottom,the key is not doing too many plants when growing Big plants ,I do two in my room .You just have to make sure that you are getting good light right down to the bottom and right round the plant ,I tie side branches down early in veg,this lets them get more light ,then round about week 4 of flower i un tie them.
There are so many answers to this question its a hard one you could do a scrog ,sog cage grow its up to you ,just get on with it dude,you will learn more from your first grow ,whats will be best ,The height you have is pretty much what i have 7 ft ,but i braced the rafters and that is where my filter now sits,On that brace.
Try a few plants ,Flower them at 12 inch ,and put a table over them ,this is by far the easiest way to hit good weights,with out the worry of height issues.You want a bit of space around each plant so light can get down to the lower nugs early on in flower.Just go for it dude
The reason i said go with a scrog is you don't have to worry about the lower stuff ,its all taken away any how,You want to get a nice weight from your start or its off putting ,I know a Grower that does one plant in just over 1 1/2 mtr x 1 1/2 mtr squared 7 ft height and he all ways hits a lb from that ,He uses HPS Light though ,same has i do in flower,all though i still get not too bad weight from LED ;Light,I have just got a better LED,and it seems to doing really well ,if i can get a nice weight from that then i will be doing a way with hps lighting.
Too many factors involved for me to say how much you will get ,but if you know your stuff then it should be a tidy weight ,with the size room you have.Lets face it Has long has that grow weight wise last you till your next grow Jobs a good en ,Stop's the Little dicks from selling 0.8 gram for 10 quid to smokers ,