20 x 12 Georgian style summerhouse garden shed

This timelapse shows the installation of a 20 x 12 summerhouse garden shed onto a concrete base that wasn't level. Using 4x2 tanalised timber and a series of treated legs the floor frame makes a level floor, saving the client the cost of having to rip up and re-lay new concrete.
Floor - levelled 45mmx 95mm (4 x 2) tanalised timbers on levelling legs, covered with 18mm exterior grade plywood
Cladding - ex19mm (16mm finished) thick redwood pine tongue and groove, 5th grade or better
Framing - 63mm x 38mm finished (3 x 2 CLS) C16 graded
Roof - ex16mm (12mm finished) redwood tongue and groove, 5th grade or better
Roof covering - Oki felt shingles, red
Treatment - Barrettines Wood Protective Treatment , Nourish and protect, light brown

[Essexhumbleorganix]

Hi how much would concrete base be and could you do that ?