I ran some tests regarding the construction and repairing of buildings and here are my results. There are some interesting outcomes.
Repair rates (HP repaired per second)
(Tested for all buildings, including wall, paliside wall, tower, TC, castle)
100 hp in 8 seconds with 1 ville = 12.5 hp/s/v
100 hp in 5 seconds with 2 villes = 10 hp/s/v
100 hp in 4 seconds with 3 villes = 8.5 hp/s/v
100 hp in 3 seconds with 4 villes = 8.1 hp/s/v
Unit damage (HP reduced per second)
2 knights with 11 attack = 22 attack
HP lost in 10 seconds
Castle = 35 HP = 3.5 hp/s
Barracks = 140 HP= 14 hp/s
TC = 100 HP= 10 hp/s
Tower = 140 HP
Paliside = 100 HP
Wall = 35 HP
Thus, one villager can repair much more effectively than one knight can attack a building. The effectiveness of units will differ (with swordsmen line having bonus damage to buildings).
Repair Costs
(Repair cost is calculated as resources required to repair the building from 1 hp)
Castle
Repair cost = 325 stone
Actual cost = 650 stone
Castle (Franks)
Repair cost = 244 stone
Actual cost = 488 stone
Lumber camp
Repair cost = 50 wood
Actual cost = 100 wood
Barracks
Repair cost = 90 wood
Actual cost = 175 wood
Watch tower
Repair cost = 13 wood + 63 stone
Actual cost = 25 wood + 125 stone
TC
Repair cost = 551 wood + 0 stone
Actual cost = 275 wood + 100 stone
TC (Britons castle age – 50% lesser wood for TC)
Repair cost = 551 wood + 0 stone
Actual cost = 138 wood + 100 stone
Conclusions
It is pointless to attack a building being constructed. Attacking does not slow down construction. Once the building is constructed, it can be repaired with half the resources. Better attack the villager building it. However, unless you can attack all the villagers simultaneously, they will still get the building ready.
Always try to repair damaged buildings. Repairing a castle that is under fire costs half the stone needed to build a new one.
NOTE: Repairing a TC takes only WOOD. However, it takes more than double the wood needed to build a new TC (551 wood to repair from 0 hp when a new one costs only 275 wood). Therefore, if you have excess of stone (1000+) and low on wood, let your TC fall and build a new one in its place. Further, building a new TC is faster than repairing an almost destroyed TC.
If you are playing Britons, NEVER repair your TC if you have enough stone. You will need the wood for building archers and repairing an almost destroyed TC needs 4 times more wood than a new one!
NOTE: Even though repairing a TC needs only wood, YOU NEED at least 1 STONE in your resource pile to start repairing.
Deleting a building under construction
If 50% has been constructed, then you will lose 50% of the resources when deleting it. i.e., if you have built 90% of the building, you will almost lose everything. This applies even if they building was not attacked at any point during its construction.
ATTACKING A BUILDING UNDER CONSTRUCTION HAS NO EFFECT ON RESOURCES LOST ON DELETING IT.
For example, if you are constructing a castle and it is at 50% complete, it will have 2400/4800 hp. If you delete it, you will get back 325 stone (50% of 650). This applies regardless of whether the building was under attack. Now, when the castle was at 50% complete, two rams are attacked it and its hp has come down from 2400 to 100. At this point if you delete your castle, you will get back 325 stone. This is another reason why there is no use in attacking a building being constructed.
Now if the rams are destroyed and then the castle is completed, it will be built with 2500/4800 hp (including the 2300 damage it suffered from the rams) However, it can be repaired now and you will need only 162 stone to bring it back to full hp (to repair 50% hp, you need only half of 50% (i.e. 25%) of 650 stone for a full building). NOTE: this applies even if you were constructing the castle while the rams were attacking.
Repair rates (HP repaired per second)
(Tested for all buildings, including wall, paliside wall, tower, TC, castle)
100 hp in 8 seconds with 1 ville = 12.5 hp/s/v
100 hp in 5 seconds with 2 villes = 10 hp/s/v
100 hp in 4 seconds with 3 villes = 8.5 hp/s/v
100 hp in 3 seconds with 4 villes = 8.1 hp/s/v
Unit damage (HP reduced per second)
2 knights with 11 attack = 22 attack
HP lost in 10 seconds
Castle = 35 HP = 3.5 hp/s
Barracks = 140 HP= 14 hp/s
TC = 100 HP= 10 hp/s
Tower = 140 HP
Paliside = 100 HP
Wall = 35 HP
Thus, one villager can repair much more effectively than one knight can attack a building. The effectiveness of units will differ (with swordsmen line having bonus damage to buildings).
Repair Costs
(Repair cost is calculated as resources required to repair the building from 1 hp)
Castle
Repair cost = 325 stone
Actual cost = 650 stone
Castle (Franks)
Repair cost = 244 stone
Actual cost = 488 stone
Lumber camp
Repair cost = 50 wood
Actual cost = 100 wood
Barracks
Repair cost = 90 wood
Actual cost = 175 wood
Watch tower
Repair cost = 13 wood + 63 stone
Actual cost = 25 wood + 125 stone
TC
Repair cost = 551 wood + 0 stone
Actual cost = 275 wood + 100 stone
TC (Britons castle age – 50% lesser wood for TC)
Repair cost = 551 wood + 0 stone
Actual cost = 138 wood + 100 stone
Conclusions
It is pointless to attack a building being constructed. Attacking does not slow down construction. Once the building is constructed, it can be repaired with half the resources. Better attack the villager building it. However, unless you can attack all the villagers simultaneously, they will still get the building ready.
Always try to repair damaged buildings. Repairing a castle that is under fire costs half the stone needed to build a new one.
NOTE: Repairing a TC takes only WOOD. However, it takes more than double the wood needed to build a new TC (551 wood to repair from 0 hp when a new one costs only 275 wood). Therefore, if you have excess of stone (1000+) and low on wood, let your TC fall and build a new one in its place. Further, building a new TC is faster than repairing an almost destroyed TC.
If you are playing Britons, NEVER repair your TC if you have enough stone. You will need the wood for building archers and repairing an almost destroyed TC needs 4 times more wood than a new one!
NOTE: Even though repairing a TC needs only wood, YOU NEED at least 1 STONE in your resource pile to start repairing.
Deleting a building under construction
If 50% has been constructed, then you will lose 50% of the resources when deleting it. i.e., if you have built 90% of the building, you will almost lose everything. This applies even if they building was not attacked at any point during its construction.
ATTACKING A BUILDING UNDER CONSTRUCTION HAS NO EFFECT ON RESOURCES LOST ON DELETING IT.
For example, if you are constructing a castle and it is at 50% complete, it will have 2400/4800 hp. If you delete it, you will get back 325 stone (50% of 650). This applies regardless of whether the building was under attack. Now, when the castle was at 50% complete, two rams are attacked it and its hp has come down from 2400 to 100. At this point if you delete your castle, you will get back 325 stone. This is another reason why there is no use in attacking a building being constructed.
Now if the rams are destroyed and then the castle is completed, it will be built with 2500/4800 hp (including the 2300 damage it suffered from the rams) However, it can be repaired now and you will need only 162 stone to bring it back to full hp (to repair 50% hp, you need only half of 50% (i.e. 25%) of 650 stone for a full building). NOTE: this applies even if you were constructing the castle while the rams were attacking.