By Julia Symmes Cobb and Nelson Bocanegra

YARI PLAINS, Colombia (Reuters) - Hundreds of FARC rebels are converging on a camp in southern Colombia to pour cement, shore up dirt roads and set up communications ahead of the group's congress this week, where delegates will ratify a peace deal to end 52 years of war.

Representatives from each unit of the Revolutionary Armed Forces of Colombia (FARC) will debate and vote on the accord reached last month after years of talks with the government.

As many as 1,000 delegates and media are expected at the 10th congress from Saturday, where rebels will discuss the five-point accord and their imminent entry into politics. Historically secretive, this congress is the first one open to civilians.

The grassy plain, about five hours drive on mud roads from the nearest large town, is being prepped with toilets and large wooden structures for dining and other events at the week-long meeting. Visitors will sleep in tents and lean-tos.

Fighters accustomed to bombing raids were laying bricks and lashing together bamboo stalks for roofing when Reuters visited the site before the official opening of the conference.

"We're working 24 hours a day in three shifts so we can be ready, given the peace process accelerated and the date surprised us a bit," Carlos Antonio Lozada, a member of the FARC's seven-member ruling committee, told Reuters.

With shirts wrapped around their heads, rebels mixed cement with sticks as two dozen reinforcements, carrying Kalashnikov rifles, arrived by truck.

The congress will mark the group's final meeting as a guerrilla army and offer hints of its political future. A preliminary agenda seen by Reuters showed delegates would discuss rural reform and political prisoners.

Previous congresses, to decide battle strategy, were sometimes held via internet due to military offensives that prevented leaders meeting.

Under the peace accord, which will be decided nationally at an Oct. 2 plebiscite, ex-rebels will be able to run for office once they complete demobilization requirements.

Marquees have been set up for the press, meals will be provided for $30 a day and an already struggling internet connection is tasked with providing Wi-Fi.

The rural location means logistics will be tricky. Roads are thick with mud and heavy rains could make them impassible.

Already, FARC fighters are busy laying wooden planks over the mud to fend off wash-outs and prevent trucks and buses getting bogged down.

"We really need two lanes," joked Dairon, his nom de guerre, as he supervised the rudimentary roadworks.

(Reporting by Julia Symmes Cobb and Nelson Bocanegra; Editing by Helen Murphy and James Dalgleish)