She is your pot of gold.

Hey there threm! Welcome to YWS! you'll have great joy here.
I'm Kat, by the way! And I'm here to review this delightful piece!
On to it

Give her a thousand roses, for all I care
Serenade her on top of your lungs
Kiss her as long as you can
And love her with all the heart you have left

So, the first thing I noticed was that there is no punctuation! Many people think that poems don't need punctuation; well, they're wrong. The basic scheme for a four line stanza is:
,
;
,
.

This will work on this stanza.
Then the capitalizing. As there is no punctuation, it doesn't seem bad. But if you put pucntuation. I would advise you to dis-capitalize the second and forth line.
The second line is awkward. Try to reword it, dear.

Open her doors for her;
Be the perfect gentleman.
Steal sugar-coated glances,
and be her number one fan.

Again, not punctuation. My thoughts on this one are in bold. In the first line, replace the first her with the and make "doors" singular (like door).

Love her with all your heart left,
I can’t change what your heart already felt.
Hold her hand all the time,
claim her heart, and don’t let her cry.

My thoughts are in bold. The first line would sound better without the left. In the second one replace already with has. It sounds better.
Three done!

Climb a rainbow,
catch all the rain!
Trap a lightning in a bottle;
do the impossible things.

This I'll have to say it's my favorite stanza. I'm not really sure about the exclamation point and the semi-colon, but I think it's rightly placed. I have no more comments on this one.

Color the sky green,
Wash the oceans red.
Loving you is possible,
But looking at it doesn’t seem real.

So, the two first lines are wonderful imagery. The third isn't bad either, but the forth one seems bad worded. try to reword it.

The Rhyming
This poem has some rhyming, but doesn't has a definite rhyming scheme, which can be good or bad. i can't really evaluate on this one.

Overall: Nicely done, my friend.

PM me if you need anything!
*Kat*