We have recently published several new resources to help developers build reporting calls to the API:
1. 
Metrics and dimensions reference pages, with each defined by the relevant values, formats and limits.
2. New 
metadata calls in the AdSense Management API V1.3 that allow developers to fetch the list of available dimensions and metrics, check compatibility between each other and find out what products are supported. A sample response might be:
{
  "kind": "adsense#reportingMetadataEntry",
  "id": "EXAMPLE_DIMENSION",
  "compatibleDimensions": [
    "1",
    "2",
    "4",
    ...
  ],
  "compatibleMetrics": [
    "AD_REQUESTS",
    "AD_REQUESTS_COVERAGE",
    "AD_REQUESTS_CTR",
    ...
  ],
  "supportedProducts": [
    "AFMC",
    "AFC",
    "AFV"
  ]
},
The 
compatibleDimensions field shows a list where each item is an integer representing a group of compatible dimensions. As there is no one-to-one relation between compatible dimensions, they are represented as groups (as shown below).
 Examples
  | Group #1 | Group #2 | Group #3 | Group #4 | 
  | AD_CLIENT_ID AD_FORMAT_CODE
 AD_FORMAT_NAME
 
 
 
 
 
 BID_TYPE_CODE
 BID_TYPE_NAME
 
 
 
 
 
 
 
 DATE
 DOMAIN_NAME
 MONTH
 PLATFORM_TYPE_CODE
 PLATFORM_TYPE_NAME
 PRODUCT_CODE
 PRODUCT_NAME
 TARGETING_TYPE_CODE
 TARGETING_TYPE_NAME
 WEEK
 | AD_CLIENT_ID AD_FORMAT_CODE
 AD_FORMAT_NAME
 
 
 
 
 
 BID_TYPE_CODE
 BID_TYPE_NAME
 
 
 
 
 
 BUYER_NETWORK_ID
 BUYER_NETWORK_NAME
 DATE
 
 MONTH
 PLATFORM_TYPE_CODE
 PLATFORM_TYPE_NAME
 PRODUCT_CODE
 PRODUCT_NAME
 TARGETING_TYPE_CODE
 TARGETING_TYPE_NAME
 WEEK
 | AD_CLIENT_ID AD_FORMAT_CODE
 AD_FORMAT_NAME
 AD_UNIT_CODE
 AD_UNIT_ID
 AD_UNIT_NAME
 AD_UNIT_SIZE_CODE
 AD_UNIT_SIZE_NAME
 BID_TYPE_CODE
 BID_TYPE_NAME
 COUNTRY_CODE
 COUNTRY_NAME
 
 
 
 
 
 DATE
 
 MONTH
 PLATFORM_TYPE_CODE
 PLATFORM_TYPE_NAME
 PRODUCT_CODE
 PRODUCT_NAME
 TARGETING_TYPE_CODE
 TARGETING_TYPE_NAME
 WEEK
 | AD_CLIENT_ID AD_FORMAT_CODE
 AD_FORMAT_NAME
 
 
 
 
 
 BID_TYPE_CODE
 BID_TYPE_NAME
 COUNTRY_CODE
 COUNTRY_NAME
 CUSTOM_CHANNEL_CODE
 CUSTOM_CHANNEL_ID
 CUSTOM_CHANNEL_NAME
 
 
 DATE
 
 MONTH
 PLATFORM_TYPE_CODE
 PLATFORM_TYPE_NAME
 PRODUCT_CODE
 PRODUCT_NAME
 TARGETING_TYPE_CODE
 TARGETING_TYPE_NAME
 WEEK
 | 
From the previous table, note that:
- DATE, MONTH and WEEK are compatible with every group. 
- DOMAIN_NAME (Group #1) is not compatible with CUSTOM_CHANNEL_* (Group #4). 
- If you want to report on ad units (Group #3) you won’t be able to use custom channels since a custom channel can be applied to one or more ad units. 
- Country names (Group #3) can be used in combination with ad units (Group #3) or custom channels (Group #4) but ad units cannot be combined with custom channels. 
Remember to visit the 
AdSense API forums or our 
Google+ page if you need any help generating reports!