Okla. Stat. tit. 19 § 1232
When the board of county commissioners deems it necessary to construct a project, grade, pave, macadamize, chat, gravel, curb, gutter, drain, or otherwise improve any road, street, alley, avenue, lane, or any part thereof, which has been established, within the unincorporated area of such county, it shall, by resolution, require the county engineer, or if there is no county engineer, a licensed engineer whose services have been contracted for, as provided by law, to prepare preliminary plans which shall include a typical section of the contemplated work or improvement, type or types of material, approximate thicknesses and widths, a preliminary estimate of the cost of such improvement, together with the cost of any improvements or draining connections directly chargeable to the property, and an assessment plat showing the area to be assessed. The resolution may provide for one or more types of construction, and the engineer shall separately estimate the cost of each type of construction. Each estimate may be in a lump sum or by unit prices, whichever seems most desirable to said engineer, for the complete improvement. The estimate shall also include the cost of advertising, appraising, engineering, and such other expense or contingencies, including attorneys and fiscal agents fees which in the judgment of such engineer are necessary or essential to the completion of such work or improvement and the payment of the cost thereof. Should more than one road, street, avenue, alley, lane, public place, or part thereof, be included in such resolution, separate estimates as to each shall be made, and any protest or objection shall be made and considered separately. For the purpose of protest in accordance with Section 1234 of this title, disconnected parts of the same street shall be treated as separate streets.
The resolution shall also require the county assessor to prepare a preliminary assessment roll based on the cost estimates of the preliminary plans and the assessor's estimate of the apportionment of benefits to the respective lots or tracts of land.
Okla. Stat. tit. 19, § 1232