When you build a new house/business in your Kingdom, you need to ensure that there is room for it. If it doesn't fit, it will glow red, and if it does fit, it will glow green. See picture below for the difference:
If you do not have enough land, you will need to clear some trees, grass or rocks. Depending on what you are clearing, you may need to whack it more than once to completely remove it.
Depending on what level you are on, you will not have access to all of the houses/businesses, but they will begin to unlock as you Level Up.
Once you have selected your house/business, you will need to whack it more than once to complete it. See the picture below for clarification:
Once you have completed whacking the building, you will need to collect materials to finish it.
Please look at the pictures below for clarification on everything about to be mentioned.
In regards to collecting materials, if you hover your mouse over the item, you will be shown where you can collect it from, either creatures, trees, grass or rocks.
If you don’t want to use up your energy, you can ask your friends for the items by clicking on Ask Friends below the item.
Lastly, you can purchase the materials you need with diamonds (this is below each item) or you can purchase all the materials you need at once with diamonds by clicking Buy All: which you’ll see at the very bottom of the pop up.
Once you have all the necessary materials, you just need to click on finish to make it complete.