May be you can look if it is already done in ktlint-standard? If yes - simply inherit it with customizations

Only spaces are allowed for indentation and each indentation should equal to 4 spaces (tabs are not allowed).
In case you prefer using tabs - just simply configure auto change of tabs to spaces in your IDE.
Exceptions:

1. When breaking parameter list of a method/class constructor it can be aligned with 8 spaces or a parameter that was moved to a newline can be on the same level as the previous argument:

class Class(propertiesFileName: String,
            otherName: String) {

or

fun visit(
        node: ASTNode,
        autoCorrect: Boolean,
        params: KtLint.Params,
        emit: (offset: Int, errorMessage: String, canBeAutoCorrected: Boolean) -> Unit
) {

2. Operators like +/-/*/e.t.c can be indented with 8 spaces:

val abcdef = "my splitted" +
                " string"