What do as-built drawings need to look like?
There are default symbols that you use for floor plans.  Google floor plan symbology to get these.  I use Visio to do all of my stuff - I have tried the apps made for doing floor plans and they just take too much time.

Obviously contacting your local municipality is the place to start.  I will just tell you my experiences.  


they want to see the entire floor that you are affecting or attaching to not just the area that you are adding or affecting.  You can keep this to just dimensions.
they want to see all electrical
for bathrooms they want to see tub/shower dimensions, toilet dimensions (and dimension to shower/tub/vanity/walls), vanity dimensions, GFCI outlets, fan placement.
they want to see how you are going to handle new electric.  Label how each outlet is getting electric.  I usually note circuit 1,2,3,4... and label outlets 1.a, 1.b, 1.c...
every single possible dimension of the rooms you are doing everything to including distances between outlets.  Also include any built in lights.
if you are digging I usually have a blank layout with the dig pattern and where we are digging and what we are doing
location of all smoke alarms and indication if they are battery or connected
if you are touching at all any existing gas or plumbing I would have a different sheet for that.  I would include details (few paragraphs of plans), label plans to layout, and then designate and spots where I will have access panels.
if you are knocking out anything load bearing - even a few feet - I would have a note signifying what we will be using to pick up load.  Most of the time this will require an engineer sign-off.  However if you are not knocking out a whole wall but making an opening bigger I have gotten inspector sign off by drawing up a support plan with well over-engineered structure.  Sometimes I talk to inspector about this and spending an extra $50 on a header (that could probably handle double the load) can save me $500 with an architect.
if you are doing kitchens most inspectors want to see where the oven, fridge, microwave are going and how they are getting electric.  There are a lot of electrical rules for GFCI outlets and distances so they want to see if you are up to code before working.  Also if you are doing an island and it is fixed most places want an outlet on it.  Your kitchen should really have its own drawing.  Some towns want to see cabinets, some don't care.  I would just label the cabinet areas "cabinets".  If they want to know exacts you can revise.  
if you are actually building a room then you need a three dimensional drawing with wood type and layout plans.  If just finishing a basement you could just say, I am using premium pine 2x4s with treated pine for bottoms.  Might have to include how you would secure the wood to the ground.  If it is a new room outside the house this is pretty intense and I would really only do this with an architect drawing.  There are drawings needed for lower support, all windows, truss/roof system, and how it connects to house and existing roof line.   Just from experience doing your own drawing for a totally new addition to your house will probably raise huge red flags with any inspector.  I would not do this unless you have had a meeting with the inspector about this beforehand.
and I totally forgot about insulation and fireblocking.  Basically this is usually just an addendum next to your picture where you tell the exact type of insulation and where it is going.  The same goes for fire blocking.  I put these together because I often put them in the same area since I usually use Roxul to fill small gaps for fire blocking (preferred method in my area).


If I can think of more I will add on.  In summary basic drawing of the entire floor or house, and very detailed for areas where there are changes.  If you have a bathroom then that is it's own drawing (zoomed-in).  If you are digging, its own drawing.  Gas or major plumbing changes, its own drawing.  If there is a new kitchen plan, then that is its own diagram.  Then electric, smoke alarms and basic stuff should be on the main drawing.  If there is an addition to existing house, then 3-D diagram from architect/engineer.  I want everything I can going to the city.  That way they can raise any red flags before I start working.  Also it is good if you have contractors.  Giving them copies of their parts will keep them inline and raise questions before they are problems.