The main factor to be considered while preparing a detailed estimate is:

Quantity of materials:
- The quantity of materials required for a project plays a crucial role in estimating the cost.
- Estimators need to determine the accurate quantity of materials needed for various construction activities such as excavation, concrete work, masonry, plastering, etc.
- This helps in calculating the cost of materials and ensures that there are no shortages or excess materials, which can impact the overall project budget.

Availability of materials:
- The availability of materials is another important factor to consider while preparing a detailed estimate.
- Estimators need to assess the availability of materials in the local market or nearby suppliers.
- If certain materials are not readily available, alternative sources may need to be considered, which can affect the overall cost estimation.
- Additionally, the cost of materials may vary depending on their availability and market conditions.

Transportation of materials:
- The transportation of materials from the supplier to the construction site is a significant aspect of cost estimation.
- Estimators need to consider the distance between the supplier and the site, as well as the mode of transportation (e.g., truck, rail, etc.) and associated costs.
- Transportation costs can vary depending on factors such as fuel prices, labor charges, and road conditions.
- Estimators should also factor in any additional costs related to handling and unloading materials at the site.

All of the above:
- Considering all the factors mentioned above is essential for preparing an accurate and detailed estimate.
- The quantity of materials determines the overall cost of materials, while the availability of materials affects their procurement and cost.
- Transportation costs need to be included to ensure an accurate estimation of the overall project cost.
- Neglecting any of these factors can lead to cost overruns, delays, or even project failure.
- Therefore, it is crucial for estimators to take into account the quantity, availability, and transportation of materials while preparing a detailed estimate.