Here are some things to keep in mind as you decide whether and how you can afford to build a new home:
Everything will cost more than you expect or think is reasonable.
You will probably need to sign a time and materials contract, rather than a contract for a fixed price, if the construction company is nervous about working with a chemically sensitive person.
If you work with a construction company you will have 10% to 15% added to the budget. That is the company’s profit. The company may also add a smaller charge of perhaps 3% to cover their monthly expenses for worker’s compensation insurance, cell phone use, etc. If you live in an area with sales tax, you have to add that to the budget as well. In my county the combined state and local sales tax is 9.6%.
In addition to the fees you will have to pay for a building permit, you may have to pay for additional studies or evaluations to satisfy the building inspectors. I had to pay for an engineering firm to prepare the stormwater management documents and for a legal and geotechnical expert to assess the safety of the ravine.
I bought vacant land outright, thinking I would be able to use the equity to secure a construction loan to build my house. It turns out that banks do not accept vacant land as collateral.
In the end I was happy not to get a construction loan. With a construction loan the bank can review every expenditure, and I did not want to have to justify my material and design choices to yet another person who would most likely not understand chemical sensitivity.
Once your house is built, you need sufficient income or resources to cover annual payments for homeowner’s insurance and property tax assessments, both of which will probably increase over time.