The following task will print out the sizes of the top-level dependencies:

tasks.register("dependenciesWithSizes") {
    doLast {
        configurations.forEach { eachConfiguration ->
            if (eachConfiguration.canBeResolved)
                println("Configuration ${eachConfiguration.name}")
                eachConfiguration.resolvedConfiguration.firstLevelModuleDependencies.forEach { firstLevelDependency ->
                    println("t${firstLevelDependency.name}")
                    firstLevelDependency.moduleArtifacts.forEach { eachArtifact ->
                        if (eachArtifact.file.exists())
                            println("ttArtifact name: ${eachArtifact.file.name} of size: ${Files.size(eachArtifact.file.toPath())} bytes")
                        else
                            println("ttArtifact name: ${eachArtifact.file.name} (can't find file)")
                    }
                }
        }
    }
}

If you want to print out the sizes of the dependencies of those dependencies (so-called transitive dependencies) you can access them via the children property of firstLevelDependency.