Not sure what you mean with "light build". The SI (metric) unit for mass is the kilogram. For small objects, smaller units such as grams and milligrams can be used; for larger objects, the ton (= 1000 kilograms) is also used.
Metres
Potatoes are sold by the kilogram.
To measure the mm of an item you would need to use a metric ruler. The metric ruler has cm and mm on it.
centimeter
You would measure that in grams, or milligrams.
Meters
You would typically measure the mass of a snowflake in the metric unit of milligrams (mg), as snowflakes are very small and light objects.
You would use the metric unit "liters" to measure the capacity of a hot water tank.
As a potato chip is light weight I would use grams and milligrams.
Metres
You would use kilograms (kg) to measure someone's mass in metric units.
You would typically use the metric unit of centimeters to measure the growth of your hair.
You would use liters (L) to measure the volume of a soda container in the metric system.
You would use the metric unit "kilograms" to measure the weight of a bag of groceries.
Potatoes are sold by the kilogram.
A thermometer.
distance