Unfortunately, a vote to leave will not change any of this in ways that will prove satisfactory for you.
A vote to leave will suppress the economy and therefore see less business for you. This may affect unscrupulous builders in the UK, but it more than likely will not short-term. Long-term it will, but by then you may have gone bust as there will be a lot less cash in the economy.
The way to address these issues is through better policed employment legislation and business legislation. All possible.
As a scrupulous builder, I know that you will never have taken cash in hand for a job, and so you should be campaigning with our own MPs to take this issue more seriously. Unfortunately, the EU has no power in this area, but the UK government does - don't let it abdicate its responsibility.
I'm not a builder.
A vote to leave will mean less opportunity for business owners to take advantage of migrants.Will mean they will have to pay proper wages and through the books.Will mean less cash in hand and more tax paid.
I have never said we should stop ALL foreign workers coming here.
As for your predictions,as Osborne and the IMF are often getting things wrong I take little note of predictions by both camps.