Romans 1 teaches that what can be known about God, namely His power and deity:
Romans 1:18-22 (ASV) 18 For the wrath of God is revealed from heaven against all ungodliness and unrighteousness of men, who hinder the truth in unrighteousness; 19 because that which is known of God is manifest in them; for God manifested it unto them. 20 For the invisible things of him since the creation of the world are clearly seen, being perceived through the things that are made, [even] his everlasting power and divinity; that they may be without excuse: 21 because that, knowing God, they glorified him not as God, neither gave thanks; but became vain in their reasonings, and their senseless heart was darkened. 22 Professing themselves to be wise, they became fools, ...
Notice that Paul first states that he is not ashamed of the Gospel for IT is the power of God unto salvation; not what can and is known about God from the creation. Secondly, notice that the WRATH of God is revealed from the things that are perceived.
1. The existence and power of the Creator, Almighty God are clearly perceptive from the natural (created) world. And that which is perspicuous to the natural man is hated and rejected and that ALL mankind substitutes a fabricated lie for that truth.
2. Morality also is included in Natural Theology as Paul teaches in Romans 2:
Romans 2:12-16 (ASV) 12 For as many as have sinned without law shall also perish without the law: and as many as have sinned under the law shall be judged by the law; 13 for not the hearers of the law are just before God, but the doers of the law shall be justified: 14 (for when Gentiles that have not the law do by nature the things of the law, these, not having the law, are the law unto themselves; 15 in that they show the work of the law written in their hearts, their conscience bearing witness therewith, and their thoughts one with another accusing or else excusing [them]); 16 in the day when God shall judge the secrets of men, according to my gospel, by Jesus Christ.
ALL mankind knows within them that which is bad, evil, sinful because the law of God is innately known due to the fact that all are created in the image of God. But knowing what is right only brings condemnation upon men because they knowingly and willingly do those things which are contrary to the commandments of God.
Thus, natural theology exists, but it produces nothing in man which will bring him to salvation in Christ, nor even to worship God who is revealed in nature. EVERY man, woman and child from conception naturally opposes the one true God and hates what can be known about Him from what can and is naturally perceived. One must guard against building an edifice of doctrine using natural theology other than what is clearly taught in Scripture. Many have gone "off the rails" with their musings and alleged deductions from what is seen, rather than what God has revealed in His written Word. The world MUST be understood through Scripture alone for it is God's own interpretation of what He has made.