For example, many times in tc_hydro you find scouts and other classes, love to rush the capture point right off the start. This said, it is completely ridiculous NOT to build a sentry and dispenser right away that will at least help in the defending process of your capture point. Also, if your the only engineer on your team at the time, or the only engineer on defense, it is pretty much crucial that you first put up a sentry and dispenser before attempting to build up and on the top roof area.
STEP ONE BUILD TELEPORT ENTRANCE OUTSIDE SPAWN & RE-SUPPLY
Upon start of round, quickly build a teleport entrance just outside of spawn. Run back inside spawn and resupply your metal.
STEP TWO BUILD TEMPORARY DISPENSER TUCKED INTO CORNER
Quickly build a temporary dispenser tucked into the corner of the wall.
STEP THREE WHILE DISPENSER SELF BUILDS, QUICKLY GRAB SPARE METAL
As soon as the dispenser starts to build, pick up the small ammo box for metal.
STEP FOUR QUICKLY BUILD TEMPORARY SENTRY AND UPGRADE TO LEVEL 3
After picking up the small box of ammo, quickly build a temporary sentry alongside the left wall. Upgrade sentry to level 3 by running back to spawn for more metal. This way, it gives the dispenser time to store up metal, in case you really need it.
STEP FIVE RESUPPLY @ LOCKER / SPAWN & DEMOLISH TEMPORARY DISPENSER
Upon upgrading sentry to level 3, head back to spawn for full metal (or feed from dispenser prior), then demolish the temporary dispenser that was first built.
STEP SIX BUILD 2ND TEMPORARY DISPENSER AGAINST SIDE WALL
Build a second temporary dispenser alongside the wall unit, in order to get the first boost for getting up top.
STEP SEVEN ( JUMP ORDER 1/6 REFERENCE )
Quickly overlook the order in which the next jumps and steps will be taken. Many people should be able to see this and figure it out automatically, but just in case, there are steps and screens to walk you through it as well.
STEP EIGHT (1.) JUMP ONTO DISPENSER (2.) JUMP UP N' CROUCH ONTO LEDGE
First jump up and onto the dispenser, which will become a boost for jumping up to the ledge.
STEP NINE (3.) RUN, JUMP N' CROUCH ONTO ALARM / FIRE BELL
Using your professional Gordon Freeman jumping skills, perform a run-jump-crouch to the alarm / fire bell.
STEP TEN (4.) JUMP N' CROUCH UP ONTO LEDGE
While atop the alarm / fire bell, jump and crouch up to the next ledge.
STEP ELEVEN (5.) JUMP N' CROUCH UP ONTO PIPE
Simply jump from the ledge your on, to the pipe sticking out of the air unit.
STEP TWELVE (6.) JUMP N' CROUCH ONTO AIR UNIT - DROP TO ROOFING
Here, you can choose a safe route by again jumping up and onto the air conditioning unit. Or, you can choose to carefully walk around the air unit and onto the main roofing area on which you will be building. I prefer to jump up and drop down.
STEP THIRTEEN DEPLOY TELEPORT EXIT - RESUPPLY @ SPAWN - USE TELEPORT
Before building, but while holding the blue print out for the teleport exit, use the Right Mouse button (twice) to turn the blueprint 180 degrees. This way, when you come out of the teleport, you are facing your sentry and not the air unit. Build the teleport exit then head back to spawn for metal and use the teleport to get back up. Or, if you're feeling adventurous, you can always re-climb your way there. ^__^ (Sometimes that is actually quicker then waiting for the exit to finish building)
STEP FOURTEEN DEMOLISH TEMPORARY DISPENSER
Once back up on the roof area, simply demolish the latest temporary dispenser.
STEP FIFTEEN BUILD DISPENSER IN CORNER - RESUPPLY @ SPAWN - USE TELEPORT
Now that you're up here with the teleport exit and sentry gaurding below, build a new dispenser in the corner. Drop down and head back to spawn for full metal, and teleport back up.
STEP SIXTEEN DEMOLISH TEMPORARY SENTRY
After the new dispenser is up and at least a quarter to half way full, demolish the temporary sentry.
STEP SEVENTEEN BUILD SENTRY ON EDGE - RESUPPLY @ SPAWN - TELEPORT - UPGRADE
Quickly build a sentry as close to the edge of the roof as possible (for maximum field of view, and also so that the sentry can shoot down at the capture point). At this moment, I prefer to speed up the build process by hitting the wrench on the sentry while it's building. Drop down and resupply @ spawn so that it gives the dispenser time to build up its metal supply. Use the teleport entrance and upgrade the sentry up to level 3.
FINAL THOUGHTS DEFEND & REPAIR
The last thing to do is keep your buildables defended and repaired! Use this strategy guide as a basic lesson for creating your own buildable setup designs and also for coming up with your own steps that are most comfortable for you. Just remember to always have a sentry up and guarding the point! ;D