Pattern Ease

Before you start your sloper, you need to know about pattern ease.  There is wearing ease and design ease.  For the purposes of making this sloper, you will be concerned with wearing ease.  You will add the appropriate amount to your measurements before you begin drafting.  Here is a good link on adding ease to your sloper.

Once you have fitted your sloper, and you are sure your measurements are proper, you can add the design ease to make blocks to serve as a base for your other garments.You can find the amount of ease added to sewing patterns on any pattern website. Here is Butterick's Chart. They have derived these numbers by adding the wearing and design ease. For wearing ease, you can look at their fitted dress, shirt, etc. ease.

Here is the page on ease from Vogue Sewing:

So, step one: Get your measurements and add appropriate wearing ease.  Make your muslin to make sure it fits right.  You will have only one sloper.

Step two: Make other basic patterns, each with the desired amount of design ease.  You may have several different pattern blocks: fitted, semi-fitted, and loose for shirts and dresses, jackets, coats, and pants. 

Step three: Change up sleeves, necklines, closures, etc. to make different garments from each of you blocks.

UPDATES:  Here are some more ease charts.