To determine which cost is generally not included in computing the cost of inventory, it is essential to understand what constitutes inventory costs. Inventory costs typically include:

• The cost of purchase: This includes the purchase price, import duties, and other taxes, transport, handling, and other costs directly attributable to the acquisition of materials, goods, or services.
• Conversion costs: These are costs directly related to the production of goods, such as direct labor costs.
• Other costs: These include costs to bring the inventories to their present location and condition.

Let's evaluate each option against this framework:

1. Administration overheads: These costs are typically not directly related to the acquisition or production of inventory. They include costs related to the overall function of an organization, and generally, under standard accounting principles, they are not included in the cost of inventory. Therefore, this is the correct answer.
2. All cost of purchase: As explained, this cost is considered part of inventory costs as it directly relates to acquiring and preparing goods for sale.
3. Normal wastage of materials: Normal wastage is generally anticipated and factored into the cost of inventory since it is a routine part of the production process.
4. Storage cost assuming a special storage is required as part of the production process: If storage is necessary to bring the inventory to its location and condition for sale, it can be included in the inventory cost.

Hence, the correct answer is Administration overheads, as it is not related to the production or purchase process involved in bringing the inventory to its sellable form.