I would dedicate 25% TGs to offensive buildings and from there on build forts, in my experience thats normally the range where they really stop paying off around your BE anyway.
Farms 10%
Banks 10%
TGs 25%
Forts 13%
Hospies 16%
Guilds 10%
Towers 4%
Stables 11%
Dungeons 1%
Something like that would be my build. When I get 50% thievery and 10% pop, i'd really think on converting to a A/T, but then again i'm sure you can NS enough on gen with lots of 0 thief provinces running around in which case I'd just put all banks into TDs.