Republican leaders in Congress want more details from President Trump about his proposed border Wall before appropriating significant funding for the project.

They have questions about the design and how the administration would handle the rights of property owners whose land would be used to build the structure.

"What I'd like to see is a plan that we know is going to be implemented that's going to be effective before we start writing the check," said Senate Republican Whip John Cornyn (R-Texas).

Cornyn said the administration needs to spell out "a layered approach" of "infrastructure, technology and personnel."

He and House Homeland Security Chairman Michael McCaul (R-Texas), who has jurisdiction over the wall, are in negotiations with the Trump administration to figure out precisely what they have in mind.

"We'd like to see what the plan is before we write a big check," McCaul told The Hill on Thursday.

"We're in current discussions with the administration. What is it going to look like, how much is it going to cost and how are you paying for this thing?"

Asked if he has received enough information from the administration, McCaul described the talks as "a work in progress."

Senate Majority Leader Mitch McConnell (R-Ky.) said last week that it probably wouldn't make sense to build a wall - which Trump suggested during the 2016 campaign would reach between 35 and 45 feet in height - along the entire length of the 1,954-mile U.S.-Mexico border.

"There are some places along the border where that's probably not the best way to secure the border," McConnell said in an interview with Politico Playbook.

McConnell also said he didn't think that Mexico would repay the United States in some form for the wall, something Trump has vowed will happen.

One of the biggest questions surrounding the wall is how to build it through along the 1,200 miles of border running through Texas, where most of the adjacent land is privately owned.

It could take years for the federal government to litigate the eminent domain claims necessary to build the barrier.

Trump's budget submitted to Capitol Hill Thursday requests an initial installment of $4.1 billion for the wall, which Gop Leaders initially estimated would cost $12 billion to $15 billion. The total final price tag for the project could run to more than $20 billion, according to other experts.

By requesting more information about the administration's plans for a border wall, GOP leaders could buy themselves time and avoid a messy standoff with Democrats over including money for the wall in the government funding measure that must pass by the end of April to avoid a government shutdown.

Senate Democratic leaders warned this week that they would not allow the measure to pass if it includes funding for the wall.

They wrote in a letter to McConnell and Senate Appropriations Committee Chairman Thad Cochran (R-Miss.) that it would "be inappropriate" to include funding in must-pass bills needed to fund the government.

Democrats say the administration needs to answer questions about eminent domain procedures, the design and location of the wall and whether Mexico will fund any of its construction.

A senior Democratic aide reiterated Thursday that Democrats will not support a funding package to keep the government operating beyond April if it includes money for the wall.

Trump's border wall proposal creates yet another problem for GOP leaders by calling for it to be paid for initially with cuts to non-defense discretionary spending programs.

His budget asks for $3 billion in fiscal year 2017 funding to pay for initial construction of the wall and improving homeland security - $1.5 billion of that total would go toward the wall.

The president has requested an additional $2.6 billion in fiscal year 2018 funding to continue construction of the wall next year.

Trump wants the money for the wall included in the government funding package that must pass by April 28, but GOP leaders are leery of giving Democrats an excuse to block it. A government shutdown fight would distract from their efforts to repeal and replace ObamaCare and begin work on tax reform.

The White House budget request puts McConnell and Speaker Paul Ryan (R-Wis.) in a bind because it calls for offsetting half the cost of a $33 billion supplemental spending bill - which includes $30 billion for defense and $3 billion for the wall and additional homeland security measures - with cuts to non-defense programs.

Democrats say this is unacceptable because it violates the agreement of the 2015 Bipartisan Budget Act, which set the spending levels for defense and non-defense programs.

Senate Democrats wrote in their letter to McConnell and Cochran that Congress has already agreed that any extra funding "should be divided equally between defense and non-defense priorities."

"Is McConnell going to be an enabler and do what Trump wants or is he going to stand up to the president and tell him there's no way Congress can pass legislation funding the government by the end of April if it cuts non-defense programs," said a senior Democratic aide.

By delaying funding for the wall and perhaps the rest of Trump's supplemental spending request until the administration provides more details about the wall, GOP leaders may be able to sidestep a fight with Democrats in the six weeks remaining before government funding expires.

Ryan reminded reporters Thursday that "we just got the president's budget submission" and "this is the very beginning of the budget process."

"What I'm encouraged by is the notion that we're going to begin rebuilding our military, which is something we're all very worried about, the hollowing out of our military," he said.

The negotiating time leading up to the deadline to fund the government is compressed by a two-week recess that both chambers plan to take in the middle of April.

McConnell said he hoped to pass the House GOP's plan to repeal ObamaCare, the American Health Care Act, before the April recess, but that now appears unlikely as GOP senators have raised a variety of concerns with the legislation.

Some GOP senators want the legislation to undergo hearings and markups in the upper chamber, which would delay floor consideration.

Sen. Rand Paul (R-Ky.) has said the House bill will be "dead on arrival" in the Senate.