It really all depends on what type of build YOU want. Here is a list of builds. Attack Build The Attack Build consists of 24 Workshops, Forges, Subterranean Factories, Cursed Foundries plus 25 The Hatchery. This build will just about always win it's first attack unless it is grossly under the enemy's ally stats. The only thing is you'll almost always lose when defending against an attack or a spy attack. Total cost to BC with T5: 4,699,000,000,000 Balanced Build The Balanced Build consists of 24 Stables, Beastiaries, War Aviaries, Circle of Elementals plus 25 The Colony. This build will nearly always win in either attack or defense against a build, however it will usually lose against a spy attack. Total cost to BC with T5: 4,699,000,000,000 Defensive Build A Defensive Build consists of 24 Barracks, War Cathedrals, Summoning Circles, Titans Lairs plus 25 Torture Garden. These builds will nearly always win in defense, but will rarely win in an attack. Total cost to BC with T5: 4,699,000,000,000 Mixed Build A Mixed Build has so many variations. The most common one though is 8 spy buildings and 41 troop buildings. This build offers good spy defense and spy attack, as well as ok attack. Total cost to BC with T5: 4,770,000,000,000 Pure Spy Build A Pure Spy Build Consists of 24 Guilds or Stronghold of Shadows plus 25 Volarys. These builds will nearly always win in a spy attack, but have no attack troops. These builds are anonymous and serve well as OSFs but give out low plunder. Total Cost to BC with T4: 5,252,083,737,000 Hansel Build A Hansel Build consists of 23 Guilds or Stronghold of Shadows along with 1 Troop Building plus 24 Volary or 25 Volary (if troop building is on HL and is T5). Total Cost to BC with T5 (Hansel): 5,880,000,000,000 Tower Build A Tower Build consists of 24 Defensive Towers, Defensive Fortresses plus 25 Arboreal Dungeon. These builds have no troops, however, they are good for allowing free steals or scouts. These builds are very hard to win against in an attack. Total Cost to BC with T5: 3,855,000,000,000 Turtle Build Turtle Builds have lots of different variations. A turtle build is any build with higher defense then possible with full troop buildings. This build often contains lots of towers and very few troop buildings. These builds are very rare. Total cost: Will vary. War Build War builds are for players who LOVE warring. These builds particularly have a lower income, but shouldn't phase warrers. These are the brutes of KaW who plan on taking all they can from you. Most war builds consist of mostly troops/spy buildings but with 8-9 towers. Commonly 8 towers, 1 castle, 6 spy buildings, and 35 troop buildings.
The total cost is wrong fiddler. If you just think about your hansel build and pure spy build, that just means building one attack building in the lowlands instead of an SOS or guild. Their cost should be nearly identical.
And your description of a tower build is not what most people consider a tower build. Tower builds require troop buildings and have a large amount of either spy defense towers or troop defense towers, typically people say 20 towers.