You dont mention how many builders you have?
Im more or less at the end of TH8 now but here's what I did.... and what i shouldnt have done lol.
Assuming that you have 4 builders (and that your lab is already upgraded) I'd cycle through splash damage upgrades (i.e 1 lvl of wiz then 1 of mortar until maxxed).
get your DE drill up to lvl3 - its still not awesome, but its free DE
the 2 longest defence upgrades are AD and tesla (tesla moreso) so get on those as soon as possible! you have 3 levels to go and the last one is 10 days per tesla.
that leaves 1 builder to work on point defences too (again, i cycled through levels on these).
I didnt concentrate on the teslas.... so now I have a 2 week wait while they catch up! :-|
to be fair though, the lab upgrades at TH8 take significantly longer than defences so if you're a 'max everything' sort of person then you'll end up hanging around anyway.
For the Lab, I did the common sense thing of working on what I used the most first - Barbs, Archers, Drags, then spells before starting on the other purple elixir stuff. . I left the DE troops alone so that it could build up for the BK (he's now at lvl10). My theory is that this will then leave me with nothing to spend elixir on while farming for DE and walls.