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OK Here are direction for creating your own Sourdough Starter Culture. List of ingredients you will need before you start.  Organic Whole Rye Flour or Organic Whole Wheat Flour*. Water**. All Purpose White Flour. A kitchen scale. The entire process  takes exactly 7 days, and takes place at room temperature 70F (+/-5F). The amount of flour is doubled with every feeding. The amount of water added, after the first three days, depends on what hydration level you wish to end up at. I gave what I believe is the optimum hydration target of 65% for a home/casual baker (like me).

Day	Flour	Water	Total Weight	% Hydration	Incubation Time
1	100g Organic Whole Rye/Wheat	100g	200g	100	24h
2	100g Organic Whole Rye/Wheat	100g	400g	100	24h
3	200g Organic Whole Rye/Wheat	200g	800g	100	24h
4	400g All Purpose White	200g	1400g	75	12h
4	800g All Purpose White	600g	2800g	75	12h
5	1600g All Purpose White	880g	5280g	65	12h
5	3200g All Purpose White	2080g	10560g	65	12h
6	6400g All Purpose White	4160g	21120g	65	12h
6	12800g All Purpose White	8320g	42240g	65	12h
7	25600g All Purpose White	16640g	84480g	65	12h
7	51200g All Purpose White	33280g	168960g	65	12h

* - Why Organic. The reason Organic flour is crucial here is because the Yeast and some microorganisms that will make our  final culture what it is are found on the Bran of the Wheat/Rye berry. And since non organic farming methods usually employ  the use of pesticides, herbicides and all sorts of other -cides. That means there is a very high probability that these yeasts and microorganisms will be killed by those chemicals thereby preventing our sour dough culture from coming to life.

** - A note on water. Many if not all municipalities add some amount of Chlorine to the tap water. Here in Los Angeles you  can actually smell it coming out of the tap. So I recommend that the water be filtered and allowed to sit for 10 -30 minutes  to allow for some of the Chlorine to dissipate. This has worked well for me so far. Some municipalities started adding a  compound known as Chloramine to the tap water. This happens to be a bond of Ammonia and Chlorine. It is virtually  impossible to get rid of this compound from the water and it will completely obliterate everything living in the sourdough  culture. If you are unfortunate enough to live in such an area you have to use bottled water for your sourdough starter.  Which is actually not as bad as it sounds as you don't really need that much. Lastly if you live in an area with soft water,  which is quite rare, it will make it more difficult to raise the sourdough starter.

OK so if we follow the amounts given in the table we are going to end up with 168kg of starter. Probably a little too much for anyone even professional bakers. :) But I wanted to show the entire procedure and its calculations, so that everyone can understand the math. In real life what we need to do is remove a portion of our mixture with every feeding and only propagate a certain small amount, something between 100g and 200g. The portion removed can be accumulated in the refrigerator as soon as possible and can be used at a later more convenient time. It can be used in bread doughs and pancake batters. Although I would not rely on its leavening abilities. Simply add it as water and flour. Some directions for sourdough establishment call for removal and discarding. But I don't have the heart to simply throw that away. :)

Having the table above it should be easy to calculate how much of what is left is water and how much is flour, using percentages.
Here's a sample table that can be used to do an actual build. The new column, called Remove shows how much mixture to remove from the sourdough starter, before that particular feeding. As I mentioned you can simply accumulate it, daily, in a single container in your refrigerator.

Day	Flour	Water	Total Weight	% Hydration	Incubation Time
1	0	100g Organic Whole Rye/Wheat	100g	200g	100	24h
2	0	100g Organic Whole Rye/Wheat	100g	400g	100	24h
3	200g	100g Organic Whole Rye/Wheat	100g	400g	100	24h
4	200g	100g All Purpose White	30g	330g	65	12h
4	130g	100g All Purpose White	65g	365g	65	12h
5	165g	100g All Purpose White	65g	365g	65	12h
5	165g	100g All Purpose White	65g	365g	65	12h
6	165g	100g All Purpose White	65g	365g	65	12h
6	165g	100g All Purpose White	65g	365g	65	12h
7	165g	100g All Purpose White	65g	365g	65	12h
7	165g	100g All Purpose White	65g	365g	65	12h

For those who like to look ahead:
Day 1. A thin, light, white layer of tiny bubbles will form on top of your mixture. Over the course of 24 hours the odor will turn more and more sour.
Day 2. The white layer will become more pronounced, some of the bubbles will become larger, and the smell will start becoming more like a really well aged Feta left at room temperature for about a week. :)
Day 3. Will start similar to day 2. However, towards the end of the 24 hours the smell will slowly start to turn into something like Apple Cider or Apple Sauce.
Day 4. The mixture will begin showing a small rise, as the very very young yeast begins to show its legs. Towards the end of the 12 hours the smell will again be similar to Apple Cider or Apple Sauce.
Day 5. The starter will now begin to double, as the yeast is almost finished establishing itself.
Day 6. Like Day 5.
Day 7. Also like Day 5.
When the starter starts to smell like Apple Cider it means that the cultures have eaten pretty much whatever was available and are now very hungry. Please Feed! :)

By Day 5 my starter was already doubling in size. This happens after a certain number of hours after feeding. Somewhere around 2 - 4 hours. So you can actually use the starter instead of yeast at this point. However, since the flora is not yet fully developed the loaves will be paper white, however, fully risen. :)
By Day 7, you need to make a decision whether you will continue the twice a day feedings at room temperature, or place your sourdough starter in the fridge, and then feed it every 5 to 7 days.

And that's pretty much all there is to it. Let me know if you guys have any questions.