Capital gains 54f

Yes but the proportionate exemption already claimed for the said land which you want to use for commercial purpose will be again taxable as long term capital gain in the year in which you want to use.Since the exemption under 54 F is for construction of residential house and that too it must be first house otherwise no exemption will be provided under 54F if the income from such house property is taxable.

Since in case of second house even there is no income that means even it is not let out the income will be estimated on deemed basis and taxable under Income from house property head while filing the return .So in above case the house you are constructedust be first house to you in order to claim exemption on capital gains under 54 F.