How can I create drop down box for height (separated by feet and inches)?

You can add a Drop Down field to your form by simply dragging it from under the Basic fields.

Upon adding a Drop Down field to your form, simply add your options by using the Options button of this newly added field:

For example, if it is human height you are looking to ask for, you could use options like this:

5' 0"
5' 1"
5' 2"
5' 3"
5' 4"
5' 5"
5' 6"
5' 7"
5' 8"
5' 9"
5' 10"
5' 11"
6' 0"
6' 1"
6' 2"
6' 3"
6' 4"
6' 5"
6' 6"
6' 7"
6' 8"
6' 9"
6' 10"
6' 11"

Such a Drop Down field would display in the following manner on a form:

When it comes to the part asking about separating them by feet and inches, I'm not sure whether the above is what you meant, or if you wanted to separate the fields even further. If you want to have separated sections within a Drop Down field, you can haev such a separated section be enclosing it with [[ and ]] brackets.

For example, drop Down options such as this:

[[5' and above]]
5' 0"
5' 1"
5' 2"
5' 3"
5' 4"
5' 5"
5' 6"
5' 7"
5' 8"
5' 9"
5' 10"
5' 11"
[[6' and above]]
6' 0"
6' 1"
6' 2"
6' 3"
6' 4"
6' 5"
6' 6"
6' 7"
6' 8"
6' 9"
6' 10"
6' 11"

Would display in the following manner on a form:

Please let us know whether this will work to your satisfaction, or kindly provide additional information if you were looking for something else. Thank you.

Thank you.