Puter,
I agree with the others that your local appraiser gave you bad advice.
Appraisers first have to be clear on the problem to be solved. You have described your problem as wanting to know what you property would appraise for as if the improvements were complete.
The way to do that is to first write up a complete description of the improvements you propose, including sizes and specific materials to be used.
The appraiser's opinion of value would be subject to the completion of your written proposal. It would also only be valid on it's effective date. For example you wouldn't want much of a delay at all between getting the appraisal and completing the project if you are located in a declining market (which you most likely are). Come to think of it, this may have been the point your local appraiser was trying to make albeit not well.
With that information you (not the appraiser) could consider the appraised value, the cost of building your proposal, your current loan balance, and the loan terms you would likely be able to get on a future refinance (can you get 80% LTV?, More? Less?)
The appraisal will be just one factor in your decision making process.
You also seem to be wanting to know the current "as is" value of your property. In my mind this is less important to your main question but of course it can be appraised. Just be aware that this is a separate appraisal.
Furthermore, you seem to be wanting an appraiser to advise you on what effect any given specific improvement might have on the overall picture. Again, the only way for an appraiser to evaluate that would be to do another appraisal for every variation in the proposals.
Each appraisal, of course, would have to be paid for.
Your "subject to completion" appraisal, again, would be at current values. A good report will include a discussion about the pricing trends in the days, months, and maybe years leading up to the effective day of the appraisal. That market trend discussion will be valuable in your dcision making process but it can not predict the future.
The appraiser will not say, "expected to decline X% per month for the next 6 months", it will say "declined x% per month for the last 12 months."
It would be up to you to decide for yourself if that trend will stay the same in the future.
There is such a thing as an appraisal as of a future effective date but it would be very subjective and most people would not rely on it in typical situations.
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ZZ, I hope I answered your question, too.
... as of the effective date that is typically the date of site inspection. The opinion of site value, or bare land, becomes the as-is value as long as no improvements are begun.