You will report the sale proceeds on Sch C as your business receipts and enter the cost of building the house as Cost of goods sold on Sch C. You will also expense other necessary and ordinary business expense and pay tax on the net income from this activity. Note that you will also be subject to self employment tax on the net income from this activity.
Let me know if you have any question.
Please note: This advice is provided with the understanding that all the relevant facts have been provided by you. Any change in facts might affect the advice given and hence may not be relied on in such cases. Nothing contained in this reply was intended or written to be used, can be used by any taxpayer, or may be relied upon or used by any taxpayer for the purposes of avoiding penalties that may be imposed on the taxpayer under the Internal Revenue Code of 1986, as amended.
If I was an LLC how would it be reported?
If it is a single member LLC and has not made a S election than this would be reported on Sch C as a single member LLC is a disregarded entity for tax purposes.