Hi,
If you import goods from overseas and you are the importer of record then the goods will be yours when they enter the UK. If you then sell these goods to your customers then you will be making a taxable supply.
As you are making taxable supplies both as a bulider and an importer then you can register for VAT voluntarily and then have an entitlement to recover the VAT as input tax.
Please see the guidance below:
Introduction to input tax
Working out whether you need to register
As you are a sole trader then all of your supplies will then come under this VAT number and you will need to charge VAT on your construction supplies as well as the sale of goods which you have imported.
Thank you.