Smallest Five Digit Number Using Roman Numerals:
Roman numerals are a numeral system that originated in ancient Rome and are still used today in various contexts. To find the smallest five-digit number using Roman numerals from the given digits 4, 5, 0, 3, and 7, we need to understand the rules of Roman numerals and how to form numbers using them.

Rules of Roman Numerals:
- Roman numerals are represented by seven different symbols: I, V, X, L, C, D, and M.
- The symbols are combined in specific ways to represent different numbers.
- When a smaller numeral is placed before a larger numeral, it is subtracted from the larger one. For example, IV represents 4 (5-1) and IX represents 9 (10-1).
- Roman numerals do not use the concept of zero.

Analysis of Given Digits:
- The given digits are 4, 5, 0, 3, and 7.
- Since Roman numerals do not have a symbol for zero, we cannot directly include it in the number.
- We can use the digits 4, 3, and 7 to form the Roman numeral representation of the smallest five-digit number.

Forming the Smallest Five-Digit Number:
- The Roman numeral for 4 is IV (5-1).
- The Roman numeral for 3 is III.
- The Roman numeral for 7 is VII.
- Combining these Roman numerals, we get IVIIIIVII.

Conclusion:
The smallest five-digit number using Roman numerals from the given digits 4, 5, 0, 3, and 7 is IVIIIIVII. Though this number includes the digits 4, 3, and 7, it does not represent a true five-digit number due to the constraints of Roman numerals.