This paper deals with the concept of the stochastic optimization methodology for power line designing, which allows optimizing transmission network planning. The paper presents a comparison of both methods applied for selecting the best line design alternative -the deterministic economic intervals method and the stochastic approach based method, taking into account market conditions. Both methods are utilized for designing overhead power lines, including the choice of main line parameters such as tower height, type and coordinates, conductor type and cross-section, line fittings, etc. Moreover, the use of High Temperature Low Sag conductors -a part of the advanced technology -was evaluated alongside the use of conductors of the traditional type. The optimization problem is formulated as minimization of the total annual costs. The proposed methodology is tested in the developed tool, which is realized in MATLAB software by using the Monte Carlo method, and in an overhead power line designing program -PLS-CADD. Two basic case studies for verifying the proposed power line planning solution are presented in the paper.